Contact allergy to formaldehyde. Diagnosis and clinical relevance.

Preservatives are biologically active substances mainly used in water-based products to prevent the growth of
microorganisms. Most people are exposed to them on a daily basis. Formaldehyde is one of the oldest and most
commonly used preservatives. However, it is a well-known contact sensitiser in dermatitis patients.
The aims of this work were: i) to investigate the prevalence of contact allergy to formaldehyde using the baseline
patch test series; ii) to determine the optimal patch test concentration and dose for formaldehyde; iii) to study
the clinical relevance of contact allergy to formaldehyde detected by formaldehyde 2.0% (0.60 mg/cm2) but not
by formaldehyde 1.0% (0.30 mg/cm2); iv) to study the effects of low concentrations of formaldehyde on irritant
contact dermatitis in formaldehyde-allergic patients; v) to semi-quantify the formaldehyde content in skin care
products used by patients with suspected allergic contact dermatitis, and compare this with the declaration of
contents; vi) to determine whether formaldehyde-allergic patients are more exposed to formaldehyde in skin
care products than dermatitis patients without contact allergy to formaldehyde; vii) to investigate the patterns
of concomitant contact allergy to formaldehyde and formaldehyde releasers.
The findings were as follows: i) patch testing with 15 μl formaldehyde 2.0% (0.60 mg/cm2) using a micropipette
detects significantly more reacting individuals than 1.0% (0.30 mg/cm2), without a high frequency of irritant
reactions. ii) individuals who react to formaldehyde 2.0% (0.60 mg/cm2) but not to 1.0% (0.30 mg/cm2)
have a significant risk of developing an eczematous reaction when exposed to concentrations of formaldehyde
allowed by the EU Cosmetic Directive. iii) daily exposure to low concentrations of formaldehyde is sufficient to
exacerbate existing dermatitis in patients with contact allergy to formaldehyde. iv) to assess exposure and clinical
relevance in formaldehyde-allergic patients, the patients’ skin care products should be analysed, especially when
the labelling of the products does not include formaldehyde or formaldehyde-releasing preservatives.