Allergic skin reactions are very common, and it can be difficult to figure out what causes them. There are hundreds of different kinds of rashes that can be caused by many things, such as plants like poison ivy, allergic reactions to a medication or a food, or a response to an illness.
When certain substances come into contact with your skin, they may cause a rash called contact dermatitis. Irritant contact dermatitis is often more painful than itchy, and is caused by a substance damaging the part of your skin it comes into contact with. The longer your skin is in contact with the substance, or the stronger the substance is, the more severe your reaction will be. These reactions appear most often on the hands and are frequently work-related.
Allergic contact dermatitis is best known by the itchy, red, blistered reaction experienced after you touch poison ivy. This allergic reaction is caused by a chemical in the plant called urushiol. You can have a reaction from touching other items the plant has come into contact with. However, once your skin has been washed, you cannot get another reaction from touching the rash or blisters. Allergic contact dermatitis reactions can happen 24 to 48 hours after contact. Once a reaction starts, it takes 14 to 28 days to go away, even with treatment.
Nickel, perfumes, dyes, rubber (latex) products and cosmetics also frequently cause allergic contact dermatitis. Some ingredients in medications applied to the skin can cause a reaction, most commonly neomycin, an ingredient in antibiotic creams. For irritant contact dermatitis, you should avoid the substance causing the reaction. You should also avoid spilling chemicals on your skin. Gloves can sometimes be helpful. Since these reactions are non-allergic, avoiding the substance will relieve your symptoms and prevent lasting damage to your skin.
Treatment for allergic contact dermatitis depends on the severity of symptoms. Cold soaks and compresses can offer relief for the acute, early, itchy blistered stage of your rash. You may also be prescribed topical corticosteroid creams. To prevent the reaction from returning, avoid contact with the offending substance. If you and your allergist cannot determine the substance that caused the reaction, your allergist may conduct a series of patch tests to help identify it.