Section 18. Skin Disorders

Chapter 202. Diagnosis and Treatment of Skin Disorders

Topics: Introduction | Diagnosis | Treatment

Treatment

Topical drugs are a mainstay of treating skin disorders. They are applied directly to the affected area of the skin. Systemic drugs are usually taken by mouth and are distributed throughout the body. Rarely, when a high concentration of a drug is needed at the affected area, a doctor injects the drug just under the skin (intradermal injection).

Topical Preparations

The active ingredient, or drug, in a topical preparation is mixed with an inactive ingredient (vehicle). The vehicle determines the consistency of the product (for example, thick and greasy or light and watery) and whether the active ingredient remains on the surface or penetrates the skin. Depending on the vehicle used, the same drug can be placed in an ointment, cream, lotion, solution, powder, or gel. In addition, many preparations are available in different strengths (concentrations).

Creams, the most commonly used preparations, are emulsions of oil in water. They are easy to apply and appear to vanish when rubbed into the skin.

Ointments are oily and contain very little water. They are messy, greasy, and difficult to wash off. Ointments are most appropriate when the skin needs lubrication or moisture. Ointments are usually better than creams at delivering active ingredients into the skin. The same concentration of drug in an ointment may have more effect than in a cream.

Lotions are similar to creams but contain more water. They are actually suspensions of finely dispersed powdered material in a base of water or oil and water. Lotions are easy to apply and are particularly useful for cooling or drying the skin.

Solutions are liquids in which a drug is dissolved. Solutions tend to dry rather than moisturize the skin. The most commonly used liquids are alcohol, propylene glycol, polyethylene glycol, and plain water.

Powders are dried forms of substances that are used to protect areas where skin rubs against skin--for instance, between the toes or buttocks, in the armpits or groin, or under the breasts. Powders are used on skin that has been softened and damaged by moisture (macerated).

Gels are water-based substances thickened without oil or fat. The skin does not absorb gels as well as it absorbs preparations containing oil or fat.

Types of Topical Drugs

Topical drugs can be divided into several overlapping categories: cleansing agents, protective agents, moisturizing agents, drying agents, symptom-relieving agents, anti-inflammatory agents, and anti-infective agents.

Cleansing Agents: The principal cleansing agents are soaps, detergents, and solvents (a liquid substance capable of dissolving other substances). Soap is the most popular cleanser, but detergents are used as well. Certain soaps dry the skin; others have a creamy base that is nondrying.

Because baby shampoos are excellent cleansing agents and are usually gentle to the skin, they are good for cleansing wounds, cuts, and abrasions. Also, people with psoriasis, eczema, and other scaling diseases can use baby shampoos to wash away dead scaly skin. Oozing (weeping) lesions, however, should generally be cleaned only with water and gentle soaps; detergents and harsher soaps can irritate the area.

Many chemicals are added to cleansing agents. For example, some soaps have antibacterial substances added to them. Antibacterial soap does not improve hygiene or prevent disease, and routine use may disrupt the normal balance of bacteria on the skin. Antidandruff shampoos and lotions may contain zinc dipyrithione, selenium sulfide, or tar extracts to help treat flaking skin, eczema, and psoriasis of the scalp.

Solvents include petroleum jelly, which can cleanse the skin of material that cannot be dissolved with soap and water, such as tar. Small amounts of alcohol, which dissolves fats and oils, can safely be used to cleanse the skin before injections or blood drawing. Alcohol is not needed for routine skin hygiene. Other solvents, such as acetone (nail polish remover), gasoline, and paint thinner, are rarely used for skin cleansing. These solvents dissolve the skin's natural oils, causing significant drying, and may also be absorbed through the skin, resulting in poisoning. Gasoline and paint thinner are also irritating to the skin.

Protective Agents: Many different kinds of preparations help protect the skin. Oils and ointments supply an oil-based barrier that can help protect scraped or irritated skin and retain moisture. Powders may protect skin that rubs against skin or clothing. Synthetic hydrocolloid dressings protect pressure sores (bedsores, decubitus ulcers) and other areas of raw skin. Sunscreens and sunblocks reflect or filter out harmful ultraviolet light.

Moisturizing Agents: Moisturizers (emollients) restore water and oils to the skin. The best time to apply a moisturizer is when the skin is already moistened--immediately after a bath or shower, for instance. Moisturizers typically contain glycerin, mineral oil, or petrolatum and are available as lotions, creams, ointments, and bath oils. Some stronger moisturizers contain compounds such as urea, lactic acid, and glycolic acid.

Drying Agents: Excessive moisture in areas where skin rubs against skin can cause irritation and skin breakdown (maceration), particularly under hot, humid conditions. The areas most commonly affected are between the toes or buttocks, in the armpits or groin, and under the breasts. These moist areas also provide fertile breeding grounds for infections, especially with fungi and bacteria.

Talcum powder is the most commonly used drying agent. Talc absorbs moisture from the skin surface. Most of the many talc preparations vary only in their scents and packaging. Cornstarch, another good drying agent, has the disadvantage of encouraging the growth of fungi. For this reason, talc is generally preferred, except for babies, because babies sometimes accidentally inhale the powder, and cornstarch is less dangerous to breathe than talc. Solutions containing aluminum salts are drying agents.

Symptom-relieving Agents: Skin disease is often accompanied by itching. Itching and mild pain can sometimes be controlled with soothing agents such as chamomile, eucalyptus, camphor, menthol, zinc oxide, talc, glycerin, and calamine. Antihistamines, such as diphenhydramine, are sometimes included in topical preparations to relieve the itching associated with allergic reactions. Although antihistamines block certain types of allergic reactions, they sometimes actually trigger an allergic reaction when applied to the skin. Taking antihistamines by mouth does not seem to produce this type of reaction, so oral rather than topical antihistamines are preferred to relieve itching.

Anti-inflammatory Agents: Corticosteroids are the main topical drugs used to relieve inflammation (swelling, itching, and redness) of the skin. Corticosteroids are most effective for rashes caused by allergic or inflammatory reactions to poison ivy, metals, cloth, or other substances. Because they lower resistance to bacterial and fungal infections, corticosteroids usually should not be used on infected areas or wounds. However, corticosteroids are sometimes mixed with antifungal drugs to help reduce itching caused by a fungus.

Topical corticosteroids are sold as lotions, creams, ointments, and gels. Creams are most effective if rubbed in gently until they vanish. In general, the ointments are the most potent. The type and concentration of corticosteroid in the preparation determines the overall strength. Hydrocortisone is available in concentrations of up to 1% without a prescription; concentrations of 0.5% or less offer little benefit. Stronger corticosteroid preparations require a prescription. Doctors usually prescribe potent corticosteroids first, then less potent corticosteroids as the disorder improves. Generally, topical corticosteroids are applied 2 to 3 times a day in a thin layer. Where the skin is already thin, such as on the face, corticosteroids should be used sparingly and not for more than a few days (see Section 5, Chapter 67).

When a stronger dose is needed, a doctor may inject a corticosteroid just under the skin. Another way to deliver a strong dose is to apply a thin plastic film, such as household plastic wrap, over the topical corticosteroid (occlusive dressing). The plastic film increases the drug's absorption and effectiveness and is usually left on overnight. Occlusive dressings increase the penetration of corticosteroids and thereby increase their effects. Such dressings are generally reserved for disorders such as psoriasis and severe eczema.

Anti-infective Agents: Viruses, bacteria, fungi, and parasites can all infect the skin. By far, the best way to prevent such infections is by carefully washing the skin with soap and water. Stronger disinfecting agents are only used on healthy skin by nurses and doctors to disinfect their own skin and the person's skin before surgery. Once infection has occurred, it may be treated with topical or systemic drugs. The type of infection dictates which drug is given.