BMA Concise Guide to Medicine & Drugs

SKIN

The skin waterproofs, cushions, and protects the rest of the body and is, in fact, its largest organ. It provides a barrier against innumerable infections and infestations, it helps the body to retain its vital fluids, it plays a major role in temperature control, and it houses the sensory nerves of touch.

The skin consists of two main layers: a thin, tough top layer, the epidermis, and below it a thicker layer, the dermis. The epidermis also has two layers: the skin surface, or stratum corneum (horny layer) consisting of dead cells, and below, a layer of active cells. The cells in the active layer divide and eventually die, maintaining the horny layer. Living cells produce keratin, which toughens the epidermis and is the basic substance of hair and nails. Some living cells in the epidermis produce melanin, a pigment released in increased amounts following exposure to sunlight.

The dermis contains different types of nerve ending for sensing pain, pressure, and temperature; sweat glands to cool the body; sebaceous glands to lubricate and waterproof the skin; and white blood cells that help to keep the skin clear of infection.

WHAT CAN GO WRONG

Most skin complaints are not serious but may be distressing if visible. They include infection, inflammation and irritation, infestation by skin parasites, and changes in skin structure and texture (such as psoriasis, eczema, and acne).

WHY DRUGS ARE USED

Skin problems often resolve without drug treatment. Over-the-counter preparations containing drugs are available, but their use is generally discouraged without medical supervision because they could aggravate some skin conditions if used inappropriately. Prescribed drugs, including antibiotics for bacterial infections, antifungals for fungal infections, agents for skin parasites, and topical corticosteroids for inflammatory conditions, are often highly effective, however. Specialized drugs are available for conditions such as psoriasis and acne.

Many drugs are topical medications, but they must be used carefully because, like oral drugs, they can also cause adverse effects.

MAJOR DRUG GROUPS

· Antipruritics

· Topical corticosteroids

· Anti-infective skin preparations

· Drugs to treat skin parasites

· Drugs used to treat acne

· Drugs for psoriasis

· Treatments for eczema

· Drugs for dandruff

· Drugs for hair loss

· Sunscreens

Antipruritics

Itching (irritation of the skin that creates the urge to scratch), also known as pruritus, most often occurs as a result of minor physical irritation or chemical changes in the skin caused by disease, inflammation, allergy, or exposure to irritant substances. People differ in their tolerance to itching, and a person’s threshold can be altered by stress and other psychological factors.

Itching is a common symptom of many skin disorders, including eczema and psoriasis and allergic conditions such as urticaria (hives). It is also sometimes caused by a localized fungal infection or parasitic infestation. Diseases such as chickenpox may also cause itching. Less commonly, itching may also occur as a symptom of diabetes mellitus, jaundice, kidney failure, or drug reactions.

In many cases, generalized itching is caused by dry skin. Itching in particular parts of the body is often caused by a specific problem. For example, itching around the anus (pruritus ani) may result from haemorrhoids or worm infestation, while genital itching in women (pruritus vulvae) may be caused by vaginal infection or, in older women, may be the result of a hormone deficiency.

Although scratching frequently provides temporary relief, it can often increase skin inflammation and make the condition worse. Continued scratching of an area of irritated skin may occasionally lead to a vicious cycle of scratching and itching that continues long after the original cause has been removed.

Many types of medicine, including soothing topical preparations and drugs taken by mouth, relieve irritation. The main drugs in antipruritic products are local anaesthetics, topical corticosteroids, and antihistamines. Simple emollient or cooling creams or ointments, which contain no active ingredients, are often recommended, especially if there is associated dry skin.

WHY THEY ARE USED

For mild itching arising from sunburn, urticaria, or insect bites, a cooling lotion such as calamine, perhaps containing menthol, phenol, or camphor, may be the most appropriate treatment. Local anaesthetic creams are sometimes helpful for small areas of irritation, such as insect bites, but are unsuitable for widespread itching. The itching caused by dry skin is often soothed by a simple emollient. Avoiding excessive bathing and using moisturizing bath oils may also help.

Severe itching in eczema or other inflammatory skin conditions may be treated with a topical corticosteroid preparation. When the irritation prevents sleep, a doctor may prescribe an antihistamine for use at night to promote sleep as well as to relieve itching (see also sleeping drugs). Antihistamines are also often included in topical preparations for the relief of skin irritation, but their effectiveness when administered in this way is doubtful. For the treatment of pruritus ani, see drugs for rectal and anal disorders. Postmenopausal pruritus vulvae may be helped by vaginal creams containing oestrogen (see female sex hormones). Itching that is caused by an underlying illness cannot be helped by skin creams and requires treatment for the principal disorder.

HOW THEY WORK

Irritation of the skin causes the release of substances such as histamine, which cause blood vessels to dilate and fluid to accumulate under the skin; this results in itching and inflammation. Antipruritic drugs act either by reducing inflammation and thus irritation, or by numbing the nerve impulses that transmit sensation to the brain.

Corticosteroids applied to the skin reduce itching caused by allergy within a few days, but the cream’s soothing effect may produce an immediate improvement. The drugs pass into the underlying tissues and blood vessels and reduce the release of histamine, the chemical that causes itching and inflammation.

Antihistamines act within a few hours to reduce allergy-related skin inflammation. Applied to the skin, they pass into the underlying tissue and block the effects of histamine on the blood vessels beneath the skin. Taken by mouth, they also act on the brain to reduce the perception of irritation.

Local anaesthetics absorbed through the skin numb the transmission of signals from the nerves in the skin to the brain.

Soothing and emollient creams such as calamine lotion, applied to the skin surface, reduce inflammation and itching by cooling the skin. Emollient creams lubricate the skin surface and prevent dryness.

RISKS AND SPECIAL PRECAUTIONS

The main risk from any antipruritic, except simple emollient and soothing preparations, is skin irritation, and therefore aggravated itching, caused by prolonged or heavy use. Antihistamine and local anaesthetic creams are especially likely to cause a reaction, and must be stopped if they do so. Antihistamines taken by mouth to relieve itching are likely to cause drowsiness. The special risks of topical corticosteroids.

Because itching can be a symptom of many underlying conditions, self-treatment should be continued for no longer than a week before seeking medical advice.

COMMON DRUGS

Antihistamines Alimemazine, Chlorphenamine, Diphenhydramine, Hydroxyzine, Mepyramine

Corticosteroids Hydrocortisone

Local anaesthetics Benzocaine, Lidocaine, Tetracaine

Emollient and cooling preparations Aqueous cream, Calamine lotion, Cold cream, Emulsifying ointment

Other drugs Colestyramine, Crotamiton, Doxepin

Topical corticosteroids

Corticosteroid drugs (which are often simply referred to as steroids) are related to the hormones that are produced by the adrenal glands. For a full description of these drugs, see Corticosteroid drugs. Topical preparations containing a corticosteroid drug are often used to treat skin conditions in which inflammation is a prominent symptom.

WHY THEY ARE USED

Corticosteroid creams and ointments are most commonly given to relieve the itching and inflammation that are associated with skin diseases such as eczema and dermatitis. These preparations may also be prescribed for the treatment of psoriasis. Corticosteroids do not affect the underlying cause of skin irritation, and the condition is therefore likely to recur unless the substance (allergen or irritant) that has provoked the irritation is removed, or the underlying condition is treated.

A doctor might not prescribe a corticosteroid as the initial treatment, preferring instead to try a topical medicine that has fewer adverse effects (see Antipruritics).

In most cases, treatment is started with a preparation containing a low concentration of a mild corticosteroid drug. A stronger preparation may be prescribed subsequently if the first product is ineffective.

HOW THEY WORK

Irritation of the skin, caused by exposure to allergens or irritant factors, provokes white blood cells to release substances that dilate the blood vessels, making the skin hot, red, and swollen.

Applied to the skin surface, corticosteroids are absorbed into the underlying tissue. There, they inhibit the action of the substances that cause inflammation, allowing the blood vessels to return to normal and reducing the swelling.

HOW THEY AFFECT YOU

Because corticosteroids prevent the release of chemicals that trigger inflammation, conditions that are treated with these drugs improve within a few days of starting the drug. Applied topically, corticosteroids rarely cause side effects. There are, however, certain risks associated with the stronger drugs used in high concentrations.

RISKS AND SPECIAL PRECAUTIONS

Prolonged use of potent corticosteroids in high concentrations usually leads to permanent skin changes – most commonly skin thinning, sometimes resulting in permanent stretch marks. Applying them sparingly and only to the affected area minimizes this risk. Fine blood vessels under the skin surface may become prominent (a condition known as telangiectasia). Because the skin on the face is especially vulnerable to such damage, only mild corticosteroids should be prescribed for use on the face. Dark-skinned people sometimes suffer a temporary reduction in pigmentation at the site of application.

When topical corticosteroids have been used for a prolonged period, abrupt discontinuation can cause rebound erythroderma (reddening of the skin). This may be avoided by gradual dosage reduction. Corticosteroids suppress the body’s immune system, thereby increasing the risk of infection. For this reason, they are never used alone to treat skin inflammation caused by bacterial or fungal infection. However, they are sometimes included in a topical preparation also containing an antibiotic or antifungal agent (see Anti-infective skin preparations).

COMMON DRUGS

Very potent Clobetasol

Potent Beclometasone, Betamethasone, Fluocinolone, Fluocinonide, Fluticasone, Mometasone, Triamcinolone

Moderate Alclometasone, Clobetasone, Fludroxycortide, Fluocortolone

Mild Hydrocortisone

Anti-infective skin preparations

The skin is the body’s first line of defence against infection. Yet the skin can also become infected itself, especially if the outer layer (epidermis) is damaged by a burn, cut, scrape, insect bite, or an inflammatory skin condition – for example, eczema or dermatitis.

Several different types of organism may infect the skin, including bacteria, viruses, fungi, and yeasts. This section concentrates on drugs applied topically to treat bacterial skin infections and includes antiseptics, antibiotics, and other antibacterial agents. Infection by other organisms is covered elsewhere (see Antiviral drugs, Antifungal drugs, and Drugs used to treat skin parasites).

WHY THEY ARE USED

Bacterial infection of a skin wound can usually be prevented by thorough cleansing of the damaged area and the application of antiseptic creams or lotions. If infection does occur, the wound usually becomes inflamed and swollen, and pus may form. If you develop these signs, you should see your doctor. The usual treatment for a wound infection is an antibiotic taken orally, although often an antibiotic cream is also prescribed.

An antibiotic or antibacterial skin cream may also be used to prevent infection when your doctor considers this to be a particular risk (for example, in the case of severe burns).

Other skin disorders in which topical antibiotics may be prescribed include impetigo and infected eczema, bedsores, and nappy rash.

Often, a preparation containing two or more antibiotics is used to ensure that all bacteria are eradicated. The antibiotics selected for inclusion in topical preparations are usually drugs, such as aminoglycosides, that are poorly absorbed through the skin. Thus the drug remains concentrated on the surface and in the skin’s upper layers where it is intended to have its effect. However, if the infection is deep under the skin, or is causing fever and malaise, antibiotics may need to be given by mouth or injection.

RISKS AND SPECIAL PRECAUTIONS

Any topical antibiotic product can irritate the skin or cause an allergic reaction. Irritation is sometimes provoked by another ingredient of the preparation rather than the active drug, such as a preservative contained in the product. An allergic reaction causing swelling and reddening of the skin is more likely to be caused by the antibiotic itself. Any adverse reaction of this kind should be reported to your doctor, who may substitute another drug, or a different preparation.

Always follow your doctor’s instructions on how long the treatment with antibiotics should be continued. Stopping too soon may cause the infection to flare up again.

Never use a skin preparation that has been prescribed for someone else since it may aggravate your condition. Always throw away any unused medication.

BASES FOR SKIN PREPARATIONS

Drugs applied to the skin are usually contained in a preparation known as a base (or vehicle), such as a cream, lotion, ointment, gel, or paste. Many bases are beneficial on their own.

Creams These have an emollient effect. They are usually composed of an oil-in-water emulsion and are used in the treatment of dry skin disorders, such as psoriasis and dry eczema. They may contain other ingredients, such as camphor or menthol.

Ointments These are usually greasy and are suitable for treating wet (weeping) eczema and very dry chronic lesions.

Gels These are jelly-like in consistency and are often water-based. They are used increasingly for a wide variety of topical skin treatments because they are easy to apply, usually non-greasy, and more rapidly absorbed than ointments.

Barrier preparations These may be creams or ointments. They protect the skin against water and irritating substances, and may be used for nappy rash and to protect the skin around an open sore. They may contain powders and water-repellent substances, such as silicones.

Lotions These thin, semi-liquid preparations are often used to cool and soothe inflamed skin. They are most suitable for use on large, hairy areas. Preparations called shake lotions contain fine powder that remains on the skin surface when the liquid has evaporated. They encourage scabs to form.

Pastes These are ointments containing large amounts of finely powdered solids such as starch or zinc oxide. Pastes protect the skin and absorb unwanted moisture. They are used for skin conditions that affect clearly defined areas, such as psoriasis.

Collodions These are preparations that, when applied to damaged areas of the skin such as ulcers and minor wounds, dry to form a protective film. They are sometimes used to keep a dissolved drug in contact with the skin.

COMMON DRUGS

Antibiotics Bacitracin, Colistin, Framycetin, Fusidic acid, Gramicidin, Mupirocin, Neomycin, Polymyxin B

Antiseptics and other antibacterials Cetrimide, Chlorhexidine, Metronidazole, Oxytetracycline, Povidone iodine, Silver sulfadiazine, Triclosan

Drugs to treat skin parasites

Mites and lice are the most common parasites that live on the skin. One common mite causes the skin disease scabies. The mite burrows into the skin and lays eggs, causing intense itching. Scratching the affected area results in bleeding and scab formation, as well as increasing the risk of infection.

There are three types of lice, each of which infests a different part of the human body: the head louse, the body (or clothes) louse, and the crab louse, which often infests the pubic areas but is also sometimes found on other hairy areas such as the eyebrows. All of these lice cause itching and lay eggs (nits) that look like white grains attached to hairs.

Both mites and lice are passed on by direct contact with an infected person (during sexual intercourse in the case of pubic lice) or, particularly in the case of body lice, by contact with infected bedding or clothing.

The drugs most often used to eliminate skin parasites are insecticides that kill both the adult insects and their eggs. The most effective drugs for scabies are malathion and permethrin; benzyl benzoate is occasionally used. Very severe scabies may require oral ivermectin as well. For lice infestations, malathion, permethrin, and phenothrin are used.

WHY THEY ARE USED

Skin parasites do not represent a serious threat to health, but their prompt eradication is needed since they can cause severe irritation and spread rapidly if left untreated. Drugs are used to eradicate them from the body, but bedding and clothing should be disinfected to avoid the possibility of reinfestation.

ELIMINATING PARASITES FROM BEDDING AND CLOTHING

Most skin parasites may also infest bedding and clothing that has been next to an infected person’s skin. To avoid reinfestation following treatment of the body, any insects and eggs lodged in the bedding or clothing must also be eradicated.

Washing Because all skin parasites are killed by heat, washing any affected items of clothing and bedding in hot water and drying them in a hot tumble dryer is an effective and convenient method of dealing with the problem.

Non-washable items Items that cannot be washed should be isolated in plastic bags. The insects and their eggs cannot survive for long without their human hosts and die within days. The length of time they can survive, and therefore the period of isolation, varies depending on the type of parasite.

HOW THEY ARE USED

Lotions for the treatment of scabies are applied to the whole body (except the head and neck) after a bath or shower. Many people find these lotions messy to use, but they should not be washed off for 12 hours (malathion) or 48 hours (benzyl benzoate), otherwise they will not be effective. It is probably most convenient to apply malathion before going to bed. The lotion may then be washed off the following morning.

Two treatments one week apart are normally sufficient to remove the scabies mites. However, the itch associated with scabies may persist after the mite has been removed, so it may be necessary to use a soothing cream or medication containing an antipruritic drug to ease this. People who have direct skin-to-skin contact with a sufferer from scabies, such as family members and sexual partners, should also be treated with antiparasitic preparations at the same time. Head and pubic lice infestations are usually treated by applying a preparation of one of the products and washing it off with water when and as instructed by the leaflet given with the preparation. If the skin has become infected as a result of scratching, a topical antibiotic (see Anti-infective skin preparations) may also be prescribed.

RISKS AND SPECIAL PRECAUTIONS

Lotions prescribed to control parasites can cause intense irritation and stinging if they are allowed to come into contact with the eyes, mouth, or other moist membranes. Therefore, lotions and shampoos should be applied carefully, following the instructions of your doctor or the manufacturer.

Because antiparasitic drugs are topical, they do not usually have generalized effects. Nevertheless, it is important not to apply these preparations more often than directed.

COMMON DRUGS

Benzyl benzoate, Crotamiton, Dimeticone, Ivermectin, Malathion, Permethrin, Phenothrin

Drugs used to treat acne

Acne, known medically as acne vulgaris, is a common condition caused by excess production of the skin’s natural oil (sebum), leading to blockage of hair follicles. It chiefly affects adolescents but it may occur at any age, due to certain drugs, exposure to industrial chemicals, oily cosmetics, or hot, humid conditions.

Acne primarily affects the face, neck, back, and chest. The primary symptoms are blackheads, papules (inflamed spots), and pustules (raised pus-filled spots with a white centre). Mild acne may produce only blackheads and an occasional papule or pustule. Moderate cases are characterized by larger numbers of pustules and papules. In severe cases of acne, painful, inflamed cysts also develop. These can cause permanent pitting and scarring.

Medication for acne can be divided into two groups: topical preparations applied directly to the skin and systemic treatments taken by mouth.

WHY THEY ARE USED

Mild acne usually does not need medical treatment. It can be controlled by regular washing and by moderate exposure to sunlight or ultraviolet light. Over-the-counter antibacterial soaps and lotions are limited in use and may cause irritation.

When a doctor or dermatologist thinks acne is severe enough to need medical treatment, he or she usually recommends a topical preparation containing benzoyl peroxide or salicylic acid. If this does not produce an improvement, preparations containing tretinoin (a drug related to vitamin A), azelaic acid, or the antibiotics clindamycin, erythromycin, or tetracycline may be prescribed.

If acne is severe or does not respond to topical treatments, a doctor may prescribe antibiotics by mouth (usually tetracycline or minocycline). If these are unsuccessful, the more powerful vitamin A-like drug isotretinoin, taken by mouth, may be prescribed.

Oestrogen drugs may have a beneficial effect on acne. A woman with acne who also needs contraception may be given an oestrogen-containing oral contraceptive. In severe cases, a preparation containing an oestrogen and cyproterone (a drug that opposes male sex hormones) may be prescribed.

HOW THEY WORK

Drugs used to treat acne act in different ways. Some have a keratolytic effect – that is, they loosen the dead cells on the skin surface. Others work by countering bacterial activity in the skin or reducing sebum production.

Topical preparations, such as benzoyl peroxide, salicylic acid, and tretinoin, have a keratolytic effect. Benzoyl peroxide also has an antibacterial effect. Topical or systemic tetracyclines reduce bacteria but may also have a direct anti-inflammatory effect. Isotretinoin reduces sebum production, soothes inflammation, and helps to unblock hair follicles.

HOW THEY AFFECT YOU

Keratolytic preparations often make the skin sore, especially at the start of treatment. If this persists, a change to a milder preparation may be recommended. Day-to-day side effects are rare with antibiotics. Treatment with isotretinoin often causes dry and scaly skin, particularly on the lips. The skin may become itchy and some hair loss may occur.

RISKS AND SPECIAL PRECAUTIONS

Antibiotics in skin ointments may, in rare cases, provoke an allergic reaction requiring discontinuation of treatment. The tetracyclines, some of the most commonly used antibiotics for acne, have the advantage of being effective both topically and systemically. However, they are not suitable for use by mouth in pregnancy since they can affect the bones and teeth of the developing baby.

Isotretinoin sometimes increases blood lipid levels. More seriously, it is known to damage a developing baby if taken during pregnancy. Women taking this drug must use effective contraception for at least one month before treatment, during treatment, and for at least one month after stopping.

COMMON DRUGS

Topical treatments Adapalene, Azelaic acid, Benzoyl peroxide, Isotretinoin, Nicotinamide (niacin), Salicylic acid, Tretinoin

Oral and topical antibiotics Clindamycin, Doxycycline, Erythromycin, Minocycline, Tetracycline, Trimethoprim

Other oral drugs Co-cyprindiol (women only), Isotretinoin

Drugs for psoriasis

The skin is constantly being renewed; as fast as dead cells in the outer layer (epidermis) are shed, they are replaced by cells from the base of the epidermis. Psoriasis occurs when production of new cells increases while shedding of old cells remains normal. As a result, the live skin cells accumulate and produce patches of inflamed, thickened skin covered by silvery scales. In some cases, the affected area is extensive and causes severe embarrassment and physical discomfort. Psoriasis may occasionally be accompanied by arthritis, in which the joints become swollen and painful.

The underlying cause of psoriasis is not known. The disorder usually first occurs between the ages of 10 and 30 and recurs throughout life. Outbreaks may be triggered by stress, skin damage, drugs, and physical illness. Psoriasis can also recur as a consequence of the withdrawal of corticosteroid drugs.

There is no complete cure for psoriasis. Simple measures, including careful sunbathing or using an ultraviolet lamp, may help to clear mild psoriasis. An emollient cream (see Antipruritics) often soothes the irritation. When such measures fail to provide adequate relief, additional drug therapy is needed.

WHY THEY ARE USED

Drugs are used to decrease the size of affected skin areas and to reduce scaling and inflammation. Mild and moderate psoriasis are usually treated with a topical preparation. Coal tar preparations, which are available in the form of creams, pastes, or bath additives, are often helpful. Dithranol is also widely used. Applied to the affected areas, the preparation is left for a few minutes or overnight (depending on the product), before being washed off. Both dithranol and coal tar can stain clothes and bed linen. If these agents alone do not produce adequate benefit, ultraviolet light therapy in the form of regulated exposure to natural sunlight or to ultraviolet lamps (UVB) may be advised. Salicylic acid may be applied to help remove thick scale and crusts, especially from the scalp.

Topical corticosteroids may be used in difficult cases that do not respond to those treatments. They are particularly useful for the skinfold areas and may be given to counter irritation caused by dithranol. If psoriasis is very severe and other treatments have failed, specialist treatment may include more powerful drugs, such as oral vitamin A derivatives (acitretin) in courses of about six months; methotrexate, an anticancer drug; vitamin D analogues such as calcipotriol; infliximab, a monoclonal antibody; and PUVA.

PUVA

PUVA is the combined use of a psoralen drug (methoxsalen) and ultraviolet A light (UVA). The psoralen is applied topically or taken by mouth; then, some hours later, the skin is exposed to UVA, which enhances the effect of the drug on skin cells. The drug is activated by exposure of the skin to the ultraviolet light; it acts on the cell’s genetic material (DNA) to regulate its rate of division.

This therapy is given two to three times a week and produces an improvement within about four to six weeks. Possible adverse effects include nausea, itching, and painful reddening of normal areas of skin. More seriously, there is a risk of premature skin ageing and a long-term risk of skin cancer, particularly in fair-skinned people. For these reasons, PUVA therapy is generally recommended only for severe psoriasis, when other treatments have failed.

HOW THEY WORK

Dithranol and methotrexate slow down the rapid rate of cell division that causes skin thickening. Acitretin and calcipotriol also reduce production of keratin, the hard protein that forms in the outer layer of skin. Salicylic acid and coal tar remove the layers of dead skin cells. Corticosteroids and infliximab reduce inflammation of underlying skin.

HOW THEY AFFECT YOU

Appropriate treatment of psoriasis usually improves the skin’s appearance. However, since drugs cannot cure the underlying cause of the disorder, psoriasis tends to recur, even following successful treatment of a recurrence.

Individual drugs may cause side effects. Topical preparations can cause stinging and inflammation, especially if applied to normal skin. Coal tar increases the skin’s sensitivity to sunlight; excessive sunbathing or overexposure to artificial ultraviolet light may damage skin and worsen the condition.

Acitretin and methotrexate can have several serious side effects, including gastrointestinal upsets, liver damage (acitretin), and bone marrow damage (methotrexate). Both are contraindicated in pregnancy; women are advised not to become pregnant for two years after completing treatment with acitretin. Topical corticosteroids may cause rebound worsening of psoriasis when stopped.

COMMON DRUGS

Acitretin, Calcipotriol, Calcitriol, Ciclosporin, Coal tar, Dithranol, Etanercept, Hydroxycarbamide, Infliximab, Methotrexate, Methoxsalen, Salicylic acid, Tacalcitol, Tazarotene, Topical corticosteroids

Treatments for eczema

Eczema is a skin condition causing a dry, itchy rash that may be inflamed and blistered. There are several types, some of which are called dermatitis. Eczema can be triggered by allergy but often occurs for no known reason. In the long term, it can thicken the skin as a result of persistent scratching.

The most common type, atopic eczema, may appear in infancy, but many children grow out of it. There is often a family history of eczema, asthma, or allergic rhinitis. Atopic eczema commonly appears on the hands, due to detergents, and the feet, due to warm, moist conditions in enclosed footwear.

Contact dermatitis, another common form of eczema, is caused by chemicals, detergents, or soap. It may appear only after repeated exposure to the substance, but strong acids or alkalis can cause a reaction within minutes. It can also result from irritation of the skin by traces of detergent on clothes and bedding.

Allergic contact dermatitis can appear days or even years after initial contact has been made with triggers such as nickel, rubber, elastic, or drugs (e.g. antibiotics, antihistamines, antiseptics, or local anaesthetics). Sunlight can also trigger contact dermatitis following use of aftershave or perfume.

Nummular eczema causes circular dry, scaly, itchy patches to develop anywhere on the body, and bacteria are often found in these areas. The cause of nummular eczema is unknown.

Seborrhoeic dermatitis mainly affects the scalp and face (see Drugs for dandruff).

WHY THEY ARE USED

Emollients soften and moisten the skin. Oral antihistamines may be prescribed for a particularly itchy rash (topical antihistamines make the skin more sensitive and should not be used). Coal tar or ichthammol may be used for chronic atopic eczema, but topical corticosteroids may be needed to help control a flare up. Rarely, severe cases that are resistant to other treatments may need to be treated with the immunosuppressant drug ciclosporin. Oral corticosteroids may be used to treat contact dermatitis. Nummular eczema usually requires corticosteroid treatment. If it is resistant, antibiotics may be prescribed because infection is likely.

HOW THEY WORK

Emollients make the skin less dry and itchy. They are available as ointments, creams, lotions, soap substitutes, or bath oils. The effect is not long-lasting, so they need to be applied frequently. Emollients do not usually contain an active drug.

Antihistamines block the action of histamine (a chemical present in all cells). Histamine dilates the blood vessels in the skin, causing redness and swelling of the surrounding tissue due to fluid leaking from the circulation. Antihistamines also prevent histamine from irritating the nerve fibres, which causes itching.

Topical corticosteroids are absorbed into the tissues to relieve itching and inflammation. The least potent one that is effective is given. Hydrocortisone 1 per cent is often used in 1 to 2-week courses.

Oral or topical antibiotics destroy the bacteria sometimes present in broken, oozing, or blistered skin.

Ciclosporin blocks the action of white blood cells, which are involved in the immune response. The drug is given in short courses when the immune system responds inappropriately to an allergen.

RISKS AND SPECIAL PRECAUTIONS

All types of eczema can become infected, and antibiotics may be necessary. Herpes virus may infect atopic eczema. Therefore, direct contact with people who have a herpes infection, such as a cold sore, should be avoided. Emollients are generally well tolerated as are short-term topical mild corticosteroids. Ciclosporin may produce some adverse effects, however.

PREVENTING ECZEMA

Trigger substances can be identified using patch testing and avoided. PVC gloves should be worn to protect the hands from detergents. Cotton clothing should be worn next to the skin. Cosmetic moisturizers should be avoided because they usually contain perfumes and other sensitizers.

PATCH TESTING

Low concentrations of suspected substances are applied to the skin of the back and held in place with non-absorbent adhesive tape. This allows a number of potential allergens (substances that can cause an allergic reaction) to be tested at the same time. After 48 hours, the adhesive tape is removed and the skin inspected for any redness, swelling, or blistering, which would indicate a positive reaction. The skin is checked after a further 24 and 48 hours, in case the reaction has taken longer to develop.

COMMON DRUGS

Emollient and cooling preparations Aqueous cream, Calamine lotion, Cold cream, Emulsifying ointment

Antihistamines Alimemazine, Chlorphenamine, Clemastine, Diphenhydramine

Corticosteroids Hydrocortisone

Other drugs Azathioprine, Ciclosporin, Coal tar, Ichthammol, Mycophenolate mofetil, Pimecrolimus, Tacrolimus

Drugs for dandruff

Dandruff is an irritating, but harmless, condition that involves an acceleration in the normal shedding of skin cells from the scalp. Extensive dandruff is considered to be a mild form of a type of dermatitis known as seborrhoeic dermatitis, which is caused by an overgrowth of a yeast organism that lives in the scalp. In severe cases, a rash and reddish- yellow, scaly pimples appear along the hairline and on the face.

WHY THEY ARE USED

Frequent washing with a detergent shampoo usually keeps the scalp free of dandruff, but more persistent dandruff can be treated with a shampoo containing the antifungal drug ketoconazole, medicated shampoos containing zinc pyrithione or selenium sulphide, or shampoos containing coal tar or salicylic acid. Ointments containing coal tar and salicylic acid are also available. Corticosteroid gels and lotions may be needed to treat an itchy rash, especially in cases of severe seborrhoeic dermatitis or psoriasis on the scalp.

HOW THEY WORK

Coal tar and salicylic acid preparations reduce the overproduction of new skin cells and break down scales which are then washed off while shampooing. Antifungals reduce the overgrowth of yeast on the scalp by altering the permeability of the fungal cell walls. Corticosteroids help to relieve an itchy rash by reducing inflammation of the underlying skin.

COMMON DRUGS

Antifungals Ketoconazole, Pyrithione zinc

Other drugs Arachis oil, Coal tar, Corticosteroids, Salicylic acid, Selenium sulphide

Drugs for hair loss

Hair loss (alopecia) is the result of greater than normal shedding of hairs, or reduced hair production. Hair loss can be caused by a skin condition such as scalp ringworm or scalp psoriasis.

Other forms of hair loss are caused by a disorder of the follicles themselves and may be a response to illness, malnutrition, or a reaction to some drugs, such as anticancer drugs or anticoagulants. The hair loss may be diffuse or in a pattern, as in male-pattern baldness, which is caused by oversensitivity to testosterone.

WHY THEY ARE USED

If the hair loss is due to a skin disorder such as scalp ringworm, an antifungal will be used to kill the fungal growth. If male-pattern baldness is a response to the male hormone testosterone, finasteride may be used to reduce the hormone’s effect. The antihypertensive drug minoxidil can be applied to the scalp to promote hair growth.

HOW THEY WORK

Hair loss can be reversed when the underlying illness is treated or treatment is stopped. Finasteride by mouth inhibits conversion of testosterone to its more active form and reduces sensitivity to androgens. The role of minoxidil in hair growth is not fully understood, but it is thought to stimulate the hair follicles.

RISKS AND SPECIAL PRECAUTIONS

Finasteride can lead to loss of libido or erectile dysfunction. Minoxidil can be absorbed through the skin and should not be used by women of childbearing age; and anyone with a history of heart disease or hypertension should consult their doctor before using the drug.

COMMON DRUGS

Antifungals Griseofulvin, Ketoconazole, Terbinafine

Other drugs Finasteride, Minoxidil

Sunscreens

Sunscreens and sunblocks are chemicals, usually formulated as creams or oils, that protect the skin from the damaging effects of ultraviolet radiation from the sun.

People vary in their sensitivity to sunlight. Fair-skinned people generally have the least tolerance and tend to burn easily when exposed to the sun, while those with darker skin, especially brown or black skin, can withstand exposure to the sun for longer periods.

In a few cases, the skin’s sensitivity to sunlight is increased by a disease such as pellagra or herpes simplex infection. Some drugs, such as thiazide diuretics, phenothiazine antipsychotics, psoralens, sulphonamide antibacterials, tetracycline antibiotics, and nalidixic acid, can also increase the skin’s sensitivity.

Apart from sunburn and premature ageing of the skin, the most serious effect from sunlight is skin cancer. Reducing the skin’s exposure to sunlight can help to prevent skin cancers.

HOW THEY WORK

Sunlight consists of different wavelengths of radiation. Of these, ultraviolet (UV) radiation is particularly harmful to the skin. UV radiation ages the skin and causes burning. Excessive exposure to UV radiation also increases the risk of developing skin cancer. UV radiation is mainly composed of UVA and UVB rays, both of which age the skin. In addition, UVA rays cause tanning and UVB rays cause burning. Especially vulnerable are fair-skinned people and those being treated with immunosuppressant drugs. Sunscreens absorb some of the UVB radiation, ensuring that less of it reaches the skin. Sunscreens are graded using the Sun Protection Factor (SPF) which refers to the degree of protection given by a sunscreen against sunburn. SPF is a measure of the amount of UVB radiation a sunscreen absorbs; the higher the number, the greater the protection. This number only describes the protection against UVB radiation. Some sunscreens, which contain chemicals such as zinc oxide and titanium dioxide, protect against UVA radiation as well; these are often called sunblocks. Certain preparations carry a “star” classification for the UVA protection they give; the stars do not describe an absolute measure but indicate a ratio of UVA to UVB protection. Four stars means that the product gives balanced protection against both UVA and UVB. Ratings of 1, 2, or 3 stars mean that the sunscreen has more protection against UVB than UVA.

A sunscreen is particularly advisable for visitors to tropical, subtropical, and mountainous areas, and for those who wish to sunbathe, because sunscreens can prevent burning while allowing the skin to tan. Sunscreens must be applied before exposure to the sun. People with fair skin should use a sunscreen with a higher SPF than people with darker skin.

RISKS AND SPECIAL PRECAUTIONS

Sunscreens form only a physical barrier to the passage of UV radiation. They do not alter the skin to make it more resistant to sunlight. Sunscreen lotions must be applied frequently during exposure to the sun for protection to be maintained. People who are very fair skinned or are known to be very sensitive to sunlight should never expose their skin to direct sunlight, even if they are using a sunscreen, because not even sunscreens with high SPF values can give complete protection.

Sunscreens can irritate the skin, and some preparations may cause an allergic rash. People who are sensitive to some drugs, such as procaine and benzocaine and some hair dyes, might develop a rash after applying a sunscreen containing aminobenzoic acid or a benzophenone derivative such as oxybenzone.

COMMON DRUGS

Ingredients in sunscreens and sunblocks Aminobenzoic acid, Benzones, Dibenzoylmethanes, Drometizole trisiloxane, Ethylhexyl methoxycinnamate, Methylbenzylidene camphor, Mexenone, Octocrylene, Oxybenzone, Padimate-O, Titanium dioxide, Zinc oxide