FORMALDEHYDE contact allergy remains a significant concern among patients with dermatitis despite regulatory efforts to limit exposure, according to a large systematic review.
Researchers carried out a metanalysis of 158 studies involving more than 1.3 million patients with dermatitis to determine the prevalence of contact allergy to formaldehyde and five commonly used formaldehyde-releasing preservatives. Overall, 2.88% of patients had a formaldehyde contact allergy, with substantial differences observed between geographical regions.
Formaldehyde and formaldehyde-releasing preservatives have been widely used for their antimicrobial properties in everyday items like makeup and hair products and are recognised causes of allergic contact dermatitis. However, differences in exposure and regulation between countries may influence rates of sensitisation.
Researchers in Denmark searched PubMed, Embase, and Web of Science for relevant studies published up to September 30, 2025.
Across 1,347,638 patients with dermatitis, the pooled prevalence of formaldehyde contact allergy was 2.88%. Of positive reactions, 41.57% were considered clinically relevant.
Marked geographical differences were identified North America had the highest prevalence of formaldehyde contact allergy, at 6.8%. In Europe it was 2.3% and its lowest in Southeast Asia at 1.8%, making the North American rate nearly three times higher than in these regions, highlighting considerable variation in sensitisation between regions.
Rates were also elevated in South America (5.4%), Africa (5.3%), and East Asia (4.2%), although estimates for some regions were based on fewer studies.
The researchers also examined contact allergy to five formaldehyde-releasing preservatives. Prevalence was highest for bronopol at 2.76%, followed by quaternium-15 at 1.89%. Rates were 1.42% for diazolidinyl urea, 1.37% for DMDM hydantoin, and 1.20% for imidazolidinyl urea.
Among these preservatives, quaternium-15 showed the greatest clinical relevance, with 55.67% of positive reactions considered relevant to patients’ dermatitis.
Age and atopic dermatitis did not appear to substantially influence prevalence. Formaldehyde contact allergy was identified in 2.96% of children and 2.61% of adults, with no significant difference between the groups. Similarly, prevalence did not differ significantly between patients with and without atopic dermatitis.
The authors highlighted regulatory differences as a potential explanation for geographical variation. In the European Union, formaldehyde and quaternium-15 are prohibited for use in cosmetic products, while restrictions also apply to other formaldehyde-releasing preservatives.
The findings suggest that such measures may reduce population exposure and subsequent sensitisation, supporting regulation as an important strategy for preventing allergic contact dermatitis.
The researchers concluded that the substantial geographical disparities observed in formaldehyde contact allergy underline the potential effectiveness of regulatory interventions in reducing exposure to clinically important contact allergens in everyday products.
Reference
Karimian K, et al. The prevalence of contact allergy to formaldehyde and formaldehyde releasers: a systematic review and meta-analysis. Contact Dermatitis. 2026. 95(2):125–147.
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