Something touches your skin, and your immune system thinks it’s under attack. It overreacts and sends antibodies to help fight the invader, called an allergen. The result is a red, itchy rash where the substance landed, the medical term for this is contact dermatitis.
Soaps, laundry detergents, fabric softeners, shampoos — or even excessive exposure to water — can all cause contact dermatitis. Other items that can cause a reaction are metals (such as nickel, a component of stainless steel and other alloys used to make costume jewelry), adhesives, nail polish, topical medications, plants, and latex gloves.
Sometimes an allergen won’t cause a skin reaction unless the skin is also exposed to sunlight. This condition is called photoallergic contact dermatitis. It can occur with products such as shaving lotion, sunscreen, and some perfumes.