Allergic contact dermatitis is a common cause of eczema-like rashes. It is caused when an allergenic substance contacts the skin of an individual who has been sensitized (or exposed and has become allergic to) the substance. Many different substances, from metals (such as nickel) to plants (such as poison ivy) to chemicals used in lotions, detergents, nail polishes, and many other personal care products can cause allergic contact dermatitis.
Many individuals with contact allergies causing rashes may not know which chemical is the culprit – patch testing can help to determine the allergenic chemical or substance causing an individual’s rash. Patch testing is different from prick or scratch testing; pick or scratch testing tests for food allergies and causes of hives.