Background: Preservatives such as formaldehyde and formaldehyde-releasers are common causes of contact allergy.

Objectives: To examine trends in contact allergy to formaldehyde and formaldehyde-releasers in patch tested patients in Denmark over a 10-year period (2007-2016), and to investigate relevant sources of formaldehyde among the patients.

Methods: A cross-sectional registry study on patch test data from patients tested with formaldehyde and formaldehyde-releasers (N = 8463) was performed. The presence of released formaldehyde in products from formaldehyde-allergic patients was identified with chemical analyses (chromotropic acid or acetylacetone test).

Results: The prevalence of contact allergy to formaldehyde 1% was 1.5%, and ranged between 0.97% and 2.3%, with a decreasing trend in this 10-year period. Contact allergy to formaldehyde 2% was found in 2.4%, and no significant trend was observed. Quaternium-15 was the formaldehyde-releaser most often positive (0.86%). Patients allergic to formaldehyde often had simultaneous positive patch test reactions to formaldehyde-releasers (36%). Almost 63% of the patients with formaldehyde allergy used products that released formaldehyde; cosmetics were the most common sources.

Conclusions: Although contact allergy to formaldehyde 1% decreased in this 10-year time period, contact allergies to formaldehyde and formaldehyde-releasers overall remain frequent in patients. In most cases, formaldehyde-allergic patients are exposed to ≥1 products containing formaldehyde. Improved regulation on permitted amounts of free formaldehyde in cosmetics is still warranted, including direct labelling of formaldehyde when it is present in small but relevant amounts.

Keywords: chromotopic acid test; consumer products; contact allergy; formaldehyde; formaldehyde-releaser.

© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.