Contact dermatitis affects up to 20% of people and can appear as either irritant (like a chemical burn) or allergic (an immune response after years of safe use). Unlike typical allergies, it doesn’t improve with antihistamines, making patch testing the key to diagnosis.

Common culprits include nickel, preservatives, and even “natural” ingredients. Dr. Dathan Heyman shares cases—from plants to kitty litter—that highlight how hidden allergens trigger rashes, and how identifying them can bring lasting relief.