Eczema is a term for “inflammation of the skin.” Inflamed skin is itchy, red, swollen and flakey. In extreme cases it can even crack, weep and blister. Dermatitis is another name for eczema. Eczema and dermatitis are synonyms and used interchangeably.
Dermatitis can have many causes. These include allergic reactions, irritation, prolonged exposure to heat and moisture, prolonged exposure to dryness (winter), and genetic factors. For now, we will focus on rashes caused by allergic reactions.
Allergic contact dermatitis
The intense itching and blistering of allergic contact dermatitis can occur after contact with a substance that causes an allergic reaction. This substance is referred to as an “allergen.” These reactions typically appear within a few days of exposure. The reacting person must be exposed on a prior occasion for the reaction to occur.
Common allergens include: nickel, rubber, antibiotics, poison ivy, hair dyes, preservatives, chemicals used in clothing manufacturing, natural oils, ingredients in skin care products, and many others. Last week we looked at allergic rashes caused by exposure to nickel and rubber products. This week we will review other causes of allergic skin dermatitis.
Hair and clothing dyes
Most people can dye their hair without any problem. Paraphenylene-diamine (PPD) is a common ingredient in many permanent hair colors that acts as a potent allergen. PPD is commonly mixed with peroxide to activate.
Be sure to always do a small spot test with any permanent dye to make sure that you are not allergic. Most temporary colorants can be tolerated, but they still need a pre-test. Some people may also react to dyes found in some clothing.
Also, a distant relative to PPD is the anesthetic PPD. About 20 percent of people allergic to PPD have allergy problems with anesthetics like benzocaine. Henna tattoos may also now contain PPD and cause allergy problems.
Triple antibiotic ointment contains bacitracin, neomycin and Polymyxin B. All of these can cause allergic reactions, but most commonly either bacitracin or neomycin. The longer one uses these antibiotics, the more likely one is to develop an allergy to them. Consult with your dermatologist before using any over-the-counter topical antibiotic, especially long term.
Skin care products
Perfumes, fragrances, creams, lotions, and cosmetic products may cause allergic contact dermatitis. Some allergies are a result of the chemical used to fragrance a product; others may be from the ingredients used as preservatives in the product. Although many products will proclaim that they are “fragrance free “or “unscented,” they rarely are.
It is easy to determine if you can tolerate such products: Put a small amount, twice daily, on your forearm for 3-5 days and if no rash forms, it is a good indicator the product is safe for you to use without an allergic reaction. More extensive allergic contact testing can be done by your dermatologist.
Chromates contain chromium and are common sources of allergic contact dermatitis. Chromates are found in cement, match tips, leather tanning, some paints, and products that combat rust. Because chromates are found in so many products, many occupations can experience chromate allergies.
There are now hundreds of pigments used in the tattoo industry, but some of the common color pigments in tattoo ink that cause allergies are:
- Red: Cinnabar
- Yellow: Cadmium
- Blue: Cobalt
- Green: Chromic oxide
- Purple: Manganese
- White: Titanium and Zinc Oxide
Poison ivy and its relatives
Every year 30 million U.S. citizens experience dermatitis from poison ivy. Poison ivy, poison oak, and poison sumac are three related American plants of the rhus family. They contain an oil (urushiol) which is the allergen and cause of allergic contact dermatitis. A diagnostic pearl is that often the very itchy rash is composed of linear blisters, marking the area where the plant brushed up against the skin.
Allergies to these three plants may make people sensitive to certain tree oils, mango husks, pistachios and cashew shells from overseas. The skin has enzymes that naturally break down the oils over four to six hours after exposure. After that, you can’t spread the dermatitis by rubbing it or breaking blisters. The only exception is if it gets on animal fur or clothing that does not contain the enzyme to break it down, it can be touched later and cause the reaction.
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 allergic reactions. Your dermatologist can provide you with a comprehensive list of suggested alternatives.
- Treatment is directed to relieve symptoms. Topical or oral steroids, cool compresses, and other non-steroidal anti-itch medicines will be recommended by your dermatologist.
- Next it is important to investigate (contact allergy ‘Patch’ test) and identify and remove/avoid the cause of the allergic skin reaction. This information can be employed to avoid future skin reactions.
- Most allergic reactions need to be treated for three weeks.
If you suspect an allergic contact dermatitis, see your dermatologist for the appropriate evaluation and treatment.
Charles E. Crutchfield III, MD is a board-certified dermatologist and Clinical Professor of Dermatology at the University of Minnesota Medical School. He also has a private practice in Eagan, MN. He has been selected as one of the top 10 dermatologists in the U.S. by Black Enterprise magazine and one of the top 21 African American physicians in the U.S. by the Atlanta Post. Dr. Crutchfield is an active member of the Minnesota Association of Black Physicians, MABP.org.