Lanolin.

Lanolin is a weak allergen that affects only about 0.4% of Europeans, but certain groups are at higher risk: people with eczema, leg ulcers, or skin barrier issues, plus children and elderly folks. Interestingly, patch testing can give false negatives on healthy skin, meaning someone might actually tolerate lanolin fine in real life even if a test suggests otherwise. Non-Hispanic white populations show higher rates of lanolin sensitivity compared to non-Hispanic Black populations.