If you develop redness, heat, swelling and pain on your skin when you come in contact with certain substances, you may have what is known as "contact dermatitis."

Contact dermatitis is caused either by an allergy or a sensitivity (a non-allergic response) to common substances. About 80 percent of skin reactions are caused by direct contact with an irritating, harsh or dangerous chemical. Household cleaners, dish detergent and soap are everyday examples of products that also can cause irritant contact dermatitis in many people, especially with longtime use. Battery acid, drain cleaner and turpentine are chemicals that cause irritant contact dermatitis in everyone.

Your skin is one of the first places where allergy symptoms can appear. In people who have a skin allergy-allergic contact dermatitis-the immune system overreacts to normally harmless substances that come in direct contact with the skin. These substances are referred to as "allergens."

No. Eczema-also called atopic dermatitis-is a skin disorder in which an allergic response especially to foods has a role in some people, especially children. Eczema is most common in infants and children. Although all eczema is not allergy-related, people with eczema usually have a family history of one or more allergic conditions such as asthma, hay fever, hives or allergic rhinitis (runny, stuffy nose). Nonallergic factors also play a role in eczema. (See AAFA's Asthma and Allergy Answers article on, "Atopic Dermatitis" (Eczema).)

An allergic response on the skin may be the result of exposure to chemicals found in many different products and plants, including:

• Dye for your hair, clothing, leather, furs
• Nail care products, cosmetics, sunscreen
• Fragrances, perfumes
• Rubber compounds
• Topical medications
• Poison ivy, other plants
• Detergents, cleaning products
• Metals, especially nickel

Allergic contact dermatitis occurs when you become "sensitized" to a specific substance. If you are allergic to something, you may have an allergic response to it on first contact and allergy symptoms will appear within 10 days. At this point, you have become "sensitized" to that particular substance. Once you develop a specific sensitivity, even brief contact with that allergen may cause your allergic contact dermatitis to reappear within 24-48 hours.

Symptoms of allergic contact dermatitis and irritant contact dermatitis are similar and can range from mild to severe. Telltale signs are a red, itchy, swollen area or rash that may or may not have blisters. Cracking or peeling skin may follow. Symptoms usually appear on the area of the skin that has been exposed.

A skin "patch" test is used to determine the most likely substances that are causing you to have an allergic response on your skin. A complete physical and history, along with test results, will assist your doctor in making a diagnosis. To help your doctor make the most accurate diagnosis, keep a log with details related to your skin reactions such as:

• What you were doing in the 24-48 hours prior to your skin outbreak?
• Where the activity occurred (In a wooded area? Working on a hobby or handicraft project? At the beach? After cleaning the house?)
• How much of product were you using? How often?
• Where did the substance touch your skin (even places with no signs of outbreak)?
• What are your usual symptoms?
• Any previous skin reactions? To what products or situations?

You can treat milder cases of contact dermatitis yourself. Over-the-counter medications such as calamine lotion, antihistamines or cortisone creams and ointments usually will relieve your discomfort. Talk with the pharmacist about recommended products.

If you have frequent and/or severe outbreaks of contact dermatitis, consult a physician. A proper diagnosis along with identification of key allergens and stronger prescription medications will help you manage your skin allergy effectively.

Thousands of common products contain substances that can trigger an allergic response on your skin. Many times these substances can be "hidden" components of a product you are using, so be sure to read labels!

Here is a list of materials that often cause allergic contact dermatitis, along with tips to help protect against an outbreak if you have a known allergy.

FRAGRANCES and PERFUMES are found in soaps, deodorants, body creams, cosmetics, tissues (scented toilet paper!) and products whose contents include the word "fragrance." To avoid problems, use fragrance-free products. Hypoallergenic products may be helpful, but could still contain fragrance. Unscented products also may contain small amounts of fragrance, which is used to mask natural odors found in the product.

NICKEL is an element in many metal alloys. Nickel is used to coat hundreds of everyday objects such as buttons, costume jewelry and kitchen utensils. Even 14k and 18k gold contains nickel that can be drawn out by sweating, water or detergent.

To help manage nickel allergies, cover nickel-containing objects that touch your skin with clear nail polish or special sprays available from your health care provider. Your dermatologist also can provide you with a kit that allows you to test items for nickel.

Ear piercing (and body piercing) that employs earrings with nickel posts actually can set off a lifetime of nickel sensitivity. For nickel-sensitive individuals, new rashes can appear in other areas of the body whenever objects containing nickel are touched! Always use surgical steel posts to avoid developing nickel sensitivity.

People who are highly allergic to nickel should not eat foods containing traces of nickel: nuts, chocolate, beer, tea, coffee and apricots all contain nickel.

LATEX is the stretchy material used in hundreds of items that come in direct contact with the body. Waistbands, bras, condoms, surgical gloves, toys and radial tire dust particles are some of the most common places where latex is found. Because latex is used in so many products today, there are increasing reports of latex sensitivity. Besides irritating the skin, latex exposure can trigger hives, hay fever or asthma symptoms, and even life-threatening anaphylactic shock.( See the Asthma and Allergy Answer article on Latex Allergy).

If you are sensitive to latex, avoid or cover clothes that have exposed rubber. Use a lambskin and a latex condom together: layer the condoms so that the partner sensitive to latex is only exposed to lambskin. (Remember: lambskin condoms do not protect against HIV.) Be sure to tell your health care providers if you have a serious allergy to latex before they put on gloves or use other rubber and latex products!

Some fruits cross-react to latex. If you have an allergic reaction to latex or rubber, you could also react to certain fruits, including banana, avocado or chestnuts.

NAIL CARE PRODUCTS usually contain a formaldehyde resin, and many people are allergic to it. Nail polishes, nail hardeners and artificial nails can all set off an allergic reaction when hands with the wet nail product come in contact with skin. Many women experience contact dermatitis on their eyelids, face and neck because their hands touch these areas before the nail product is dry. If you use nail care products, be sure to keep your hands away from your face and neck until your nails are completely dry; use a nail-drying machine to speed up drying time.

THE SUN can be a culprit in causing skin allergies. Harmless chemicals applied to the skin are converted into "photocontact allergens" by ultraviolet rays. Alone, neither the sun nor the substance cause a reaction. But together, they produce an allergic response. Photocontact allergens often are found in topical antibiotics, cosmetics, perfumes and even sunscreen products!

You can confirm sun sensitivity with a photopatch test. Also ask your physician if any medications you are taking could cause photosensitivity. If you are allergic to sunscreen products themselves, you need to find a substitute. Look for non-PABA containing products if you are allergic to PABA or its derivatives; chemical-free sunscreens also are available.