Allergic Contact Rashes
Allergic contact dermatitis is a condition that can be caused by substances that come into contact with the skin. A substance that causes allergic contact dermatitis is called an “antigen”. If you are allergic to an allergen, then contact with that allergen to the skin can produce itching and blisters (allergic contact dermatitis). Allergic contact dermatitis is not usually caused by things such as acid, alkali, solvents, strong soap or detergent. These harsh chemicals, which can produce a reaction on anyone's skin, are known as “irritants”. Some chemicals are both irritants and allergens.
What Dermatitis Looks Like:
Usually the skin gets red, swollen, and blisters appear. The blisters may form and break, leaving crusts and scales. Later the skin may darken and become leathery and cracked. Allergic contact dermatitis can be difficult to distinguish from other rashes.
|Allergic contact dermatitis caused by poison ivy|
Discovering the Cause:
The dermatologist and patient will discuss the materials that come into contact with the person's skin at work and home to try to identify the allergen. Most contact dermatitis is diagnosed by location of the rash. Sometimes cause can not be identified by history and physical examination, and the dermatologist may want to perform a patch test. Patch tests are a safe and easy way to diagnose contact allergies. Small amounts of the possible allergens are applied to the skin on strips of tape and then removed after two days. An allergy shows up as a small red spot at the site of the patch. Common allergens include nickel, rubber, dyes, preservatives, fragrances, poison ivy, poison oak, and related plants.
Nickel, a part of certain metals, is found in many metal products. Many chrome-plated objects contain enough nickel to produce a reaction in sensitive people. Stainless steel also contains nickel, but it is bound so tightly that it is safe for most nickel-sensitive individuals. Earrings containing nickel can cause earlobe dermatitis, a very common problem in people allergic to nickel. This may start with the needles used to pierce ears, and earrings. Only sterile stainless needles should be used for piercing. After piercing, only nickel-free earrings should be worn for at least the first three weeks. Clothing fasteners made of nickel-buckles, zippers, buttons, and metal clips-can cause dermatitis. Nickel-sensitive people can substitute with nylon accessories. Sweating increases dermatitis in nickel-sensitive people. Items containing nickel can cause an itchy, prickly sensation within 15-20 minutes after touching sweaty skin. A rash may appear within a day or two. These same items can be worn for several hours without any problems, if sweat is not present.
Rubber - A Frequent Offender: Rubber products often cause allergic contact dermatitis. Chemical additives in rubber can cause the reaction. Rubber, especially latex, can also cause immediate allergic reactions, including itching, or burning and hives (welts). Some people experience itching, tearing eyes, and though rarely, shortness of breath. This is more common in people who wear tight fitting rubber gloves, such as medical workers. Rubber gloves may also cause dermatitis on the skin of the hands under the glove. Powderless rubber gloves may be less allergenic. Vinyl or other synthetic gloves may be substituted. Many women with a rubber allergy can wear undergarments made with an elastic called spandex if they do not have rubber-backed fasteners or edges. Undergarments with no rubber are available. Most cases of allergic contact dermatitis from shoes are caused by ingredients in the rubber used in the construction of the shoe. Shoes with rubber should be substituted. Adhesives in shoes can also cause problems. Even leather shoes may contain adhesives.
Hair Dyes - Most people can color their hair without difficulty. However, some are sensitive to paraphenylene-diamine (PPD). This ingredient is found in permanent hair dyes that are mixed with another chemical, such as peroxide, before application. People allergic to PPD should not use any permanent hair dyes. About one-fourth of the people allergic to PPD are also allergic to ingredients in semi-permanent dyes. Follow the package instructions for a patch test before using any hair dye. Most PPD allergic people can use temporary dyes or rinses, to blend in gray and brighten hair. A few people, however, will react to these dyes too. While PPD dyes are rare in clothing, other dyes that may cross-react with PPD may be present. As a result, some PPD-sensitive patients cannot wear dark clothing; especially clothing made of synthetic fibers like polyester or nylon. About 25% of PPD sensitive people are also allergic to certain local anesthetics, like benzocaine, that are chemical relatives of PPD.
Neomycin - Neomycin is a common allergen found in both prescription and non-prescription topical antibiotic creams, ointments, lotions, ear drops, and eye drops. It is also used in combination with other topical antibiotics, topical steroids, and in first aid creams. Neosporin, triple antibiotic creams, and ointments contain neomycin. People who are allergic to neomycin and treat their cuts, abrasions, rashes, and poison ivy dermatitis with over-the-counter creams containing neomycin, frequently develop neomycin induced dermatitis.
Skin Care Products - Perfumes, lotions, and cosmetics may cause allergic contact dermatitis. Some people are sensitive to the fragrance chemicals used in skin care products. Others are sensitive to the preservative chemicals needed to prevent skin care products from spoiling. People with a fragrance allergy can use fragrance-free products, but “unscented” products may still have a fragrance added to cover up the smell of the chemicals. There are very few truly preservative-free products, but persons may be sensitive to only one preservative chemical and not others. This can be determined by patch testing.
Chromates - Chromates contain chromium, and are commonly responsible for allergic contact dermatitis from cement, leather, some matches, paints, and anti-rust products. Contact with chromium is common in jobs in the automobile, welding, foundry, cement, railroad, and building repair industries. Chromates are used to tan leather for shoes and clothing. “Shoe dermatitis” may result from leather containing chromates. Vegetable-tanned footwear can be used as an alternative. Some matches contain chromates. Touching unlit matches can contaminate fingers. Fumes from a lit match and the charred match head also contain traces of chromates. Placing used matches or book matches in a pocket will contaminate the pocket lining.
Poison Ivy and Its Relatives - This plant family includes poison ivy, poison oak, and poison sumac. In the US , these plants produce many cases of allergic contact dermatitis. The reaction looks the same from all of them. Often patients develop lines of small blisters on the skin where the plant brushed against them. People sensitive to poison ivy, oak, and sumac are often allergic to oils from plants from other countries. A furniture lacquer obtained from the Japanese lacquer tree contains such an oil, as do mango rinds and cashew shells.
People with allergic contact dermatitis should:
- Avoid the allergen that causes the reaction, and chemicals that cross-react with it. Your dermatologist can help you identify items to avoid.
- Substitute products that do not cause reactions. Your dermatologist can suggest sources for these products.