Tough Skin Needs Tender Loving Care : Medicine: Rashes, which are often caused by allergies, can make us miserable, but there are simple ways to prevent and treat them.

The skin, the human body’s largest organ, can be thought of as a person’s first line of defense against the rest of the world; it’s a thin but remarkably tough barrier against wind, water and chemicals.

But the skin’s location on the front line of the body’s defenses also makes it especially vulnerable to irritation.

Dermatitis--literally, inflammation of the skin--is an itchy, red rash that most people have experienced at one time or another. The affected skin becomes dry and scaly and can even crack and bleed.

The condition often goes away quickly, but if you have a recurring rash, you may need to take some steps--and possibly do some detective work--to control it.

Most cases of dermatitis result from irritation by a harsh agent, like a detergent, cleaning solvents or even acid. “Dishpan hands,” caused by water or harsh detergents, is one of the most familiar forms of irritant dermatitis.

Allergic dermatitis is caused by contact with a substance that doesn’t harm skin directly but that triggers an allergic reaction.

The reaction happens when the substance or allergen is transported to nearby lymph nodes, initiating changes in the immune cells, called lymphocytes, and leading eventually to the release in the skin of various chemicals that produce inflammation and itching.

Unlike irritant dermatitis, which can affect anyone, allergic dermatitis affects only people sensitive to a specific substance. Poison ivy is the most common and familiar cause of skin allergy; others include metals and certain fruits.

If you have a recurring red, scaly rash that you can’t trace to an obvious irritant, you may be suffering from a skin allergy. For example, some people are allergic to nickel, which is often used as a base for jewelry alloys. If you develop a rash on your ear, wrist or finger when wearing jewelry, a nickel allergy may be the cause.

If the cause of the rash is not so immediately apparent, you still may be able to figure it out by keeping a record of what you are doing and with what you came in contact before it broke out.

Obviously, the most effective way to fight a skin allergy is to avoid the allergen. But if you can’t do so, if you aren’t sure what’s causing the allergic reaction or if you are exposed by accident, there are over-the-counter medications that can help.

The most effective ointments against allergic dermatitis are those that contain cortisone.

People with irritant dermatitis, such as dishpan hands, should also keep their skin moisturized with hand lotions, ointments and creams; often, petroleum jelly or hand creams will do the job. It also helps to use rubber gloves to guard against irritants like dish soap.

For a small group of people, though, using rubber gloves actually makes their skin problems worse. These people are allergic to the gloves themselves--more specifically, to latex, from which today’s rubber gloves are usually made.

Allergy to latex is relatively rare. Most often, it affects people who wear latex gloves repeatedly, such as health-care workers. There are latex-free gloves available for people with this sensitivity.

In most cases, you should be able to control either kind of dermatitis on your own. But if these protective steps and commercial remedies don’t help, seek medical evaluation. You may need a prescription-strength product.