Formaldehyde is a common contact allergen. The prognosis of formaldehyde-sensitive patients is generally considered to be bad because of widespread exposure to formaldehyde. 11 patients with eczema and a positive patch test to formaldehyde were interviewed by a dermatologist and a toxicologist/chemist and instructed to fill in a questionnaire on exposure to chemical products. The content of formaldehyde and formaldehyde releasers in such products was examined using the database of the Danish Product Register (PROBAS) and by supplemental inquiries of manufacturers or importers. All the patients used one or more products containing formaldehyde or formaldehyde releasers. Sources of exposure were cosmetics and personal care products, dishwashing liquids, water-based paints, photographic products, etc. Patients were advised to use alternatives to those products containing formaldehyde or formaldehyde releasers. The status of 10 out of the 11 patients' eczema at follow-up was about 1/3 healed, 1/3 improved and in 1/3 no change. When the relevance of positive patch test reactions to formaldehyde was based on information obtained on exposure, a very high rate of current relevance was found. Computerized data on product composition allows the screening of products for contact allergens and also generates lists of contact allergens indicated for patch testing, based on the patients' own products.