Topical agents—medicines applied to the surface of the skin—are important in the management of the symptoms of eczema. Topical agents are prescribed to reduce skin inflammation, control itching, loosen and remove scaly lesions, and in some instances to reduce formation of new lesions. Dermatologists prescribe topical agents with instructions for their use, but patients may find it difficult to understand the basis for instructions. This Update offers information that may help a patient get the maximum benefit from topical therapy.

Topical agents can be defined as single agents, combinations of two agents, or combinations of three agents. All three types may be carriers for dermatologic drugs.

Single Agents

Powders decrease friction of skin-to-skin surfaces and are used most frequently to promote drying of sweaty, or oozing lesions. A powder used frequently is zinc oxide, but it must be used as directed. If used in skin creases when the skin is "weeping," powders may form clumps that are abrasive. Powders are frequently added to other agents to make shake lotions or pastes.

Liquids are used for drying sweaty and/or oozing skin surfaces, and constitute a variety of agents that include baths, wet dressings, paints, solutions of active ingredients in an inert carrier, and gels that liquefy upon contact with the skin. Tar baths are a standard treatment for many skin conditions.

Oils are a liquid that is insoluble in water. Oils are combined with other ingredients to make oil-in-water and water-in-oil agents.

Combination of Two Agents

Shake lotions are a combination of a powder and liquid that must be shaken before application. Best applied to oozing and/or wet lesions.

Creams are emulsions of oil in water (50 percent oil and 50 percent water), that may be used as soothing emollients or an carriers for dermatologic drugs. The oil-in-water emulsion aids penetration of drugs through the stratum corneum—the horny outer layer of the skin.

Ointments are water-in-oil (80 percent oil and 20 percent water) emulsions that form a protective (occlusive) layer on the skin and are generally more lubricating (moisturizing) than creams. As carriers of dermatologic drugs, ointments generally provide better penetration of the stratum corneum than do creams and lotions. However, dermatologic drugs are compounded to be most effective in certain carriers, and thus for specific drugs creams may be more effective carriers than ointments. Because ointments are insoluble in water they are not easily washed off the skin, but easily removed with "oils."

Pastes are ointments in which powder is suspended. Pastes are drying and less greasy than ointments. They are carriers for some dermatologic drugs and can create a protective layer.

Combinations of Three Agents

Oil-water-powder combinations are sometimes used as soothing pastes on inflamed and "weeping" skin. A typical oil-water-powder combination is zinc oxide, calcium hydroxide solution, and oil.

How Often and How Much?

Topical agents are carefully compounded to provide the maximum efficacy when used at specified frequency and concentration. The carrier of the drugs—e.g., cream, ointment, or paste—is selected to provide the most effective application of the drug for the purpose intended. The most effective use of a topical agent is obtained by following the prescribed instructions for application.

Patients who are anxious to maximize a topical agent’s effectiveness may mistakenly believe that "more" and "more often" will enhance drug efficacy, leading them to apply the agent more frequently and/or in greater amount than prescribed.

Using a topical agent more frequently than prescribed carries a risk for drug 
toxicity or triggering of a side effect. Using a topical agent in greater amount than prescribed is unnecessarily wasteful and costly. Studies have shown that the penetration and effectiveness of a topical agent is not increased by applying a 
thicker layer of the agent, but it does increase the amount of the agent that eventually must be purchased. An effective "test" for proper application of a topical 
is to touch the treated area with a tissue. If an oil mark appears on the tissue, too much was applied.