The Prevalence of Contact Allergy to Formaldehyde and Formaldehyde Releasers: A Systematic Review and Meta-Analysis.

Formaldehyde and its releasers are common preservatives and potent sensitizers. This meta-analysis aimed to estimate the prevalence of formaldehyde contact allergy and allergy to its five most common releasers among dermatitis patients. Two authors independently searched PubMed, Embase, and Web of Science from inception to 30th September 2025. A proportion meta-analysis was conducted using a random-effects model. A total of 158 studies involving 1 347 638 dermatitis patients were included. The pooled prevalence of formaldehyde contact allergy was 2.88% (95% CI 2.55-3.24) with clinical relevance at 41.57%. The pooled prevalence for releasers was 2.76% for 2-bromo-2-nitropropane-1,3-diol, 1.89% for quaternium-15, 1.42% for diazolidinyl urea, 1.37% for DMDM hydantoin, and 1.20% for imidazolidinyl urea. Quaternium-15 showed the highest clinical relevance at 55.67%. Significant sensitization rates were observed in different geographic regions, with the highest prevalence found in North America (6.8%). The prevalence rate was 2.96% among children and 2.61% among adults, with no significant difference. The prevalence rate was 2.65% among patients with atopic dermatitis (AD) and 2.85% among patients without AD, with no significant difference. The profound geographic disparities suggest that regulatory interventions, such as the EU's prohibition of formaldehyde and quaternium-15 in cosmetics, are highly effective public health measures.