Most product labels list ingredients by INCI name, which is a language of its own. A handful of ingredients account for a large share of contact reactions in the general population. Here is what to look for, per public dermatology references.
Fragrance (often listed as 'fragrance' or 'parfum') is one of the most common contact allergens, per the American Academy of Dermatology (AAD). It's a catch-all term covering hundreds of compounds — if your skin reacts to many fragranced products, fragrance is the first suspect.
Preservatives are the other big group: methylisothiazolinone (MIT/MI) and its partner methylchloroisothiazolinone (MCI) are strong sensitizers linked to contact dermatitis, and formaldehyde-releasing preservatives (DMDM hydantoin, quaternium-15, diazolidinyl urea, imidazolidinyl urea) are classic allergens.
Irritation is not the same as allergy. Irritants like sodium lauryl sulfate (SLS), alcohol denat., and propylene glycol can dry or sting sensitive skin without involving the immune system. Allergens trigger a true allergic response — often delayed by hours or days.
The practical difference: irritation usually appears fast and scales with concentration; allergic reactions can appear even at tiny amounts and after repeated exposure. Both matter for choosing products.
Read the full INCI list, not just the marketing claims. Paste the list into the scanner on this page — it flags the ingredients above with their reference source. Then, for anything new to your routine, patch-test on a small area before full use.
If you have a real reaction, stop the product and see a dermatologist. A formal patch test is the only reliable way to confirm which ingredient is responsible.