The currently used patch test concentration of formaldehyde (1.0% aqua; 0.30 mg/cm(2)) has been shown to fail to detect ~ 50% of contact allergies to formaldehyde.
To justify the inclusion of formaldehyde 2.0% aqua (0.60 mg/cm(2)) in the European baseline patch test series.
A survey of the reported frequencies of contact allergy to formaldehyde found with formaldehyde 2.0% aqua as compared with 1.0% aqua was performed. Studies that describe a standardized patch test technique for obtaining a correct dose per unit area were included. Experimental provocation tests in patients with contact allergy to formaldehyde detected only with 2.0% aqua were also surveyed.
In a multicentre study performed in 12 dermatology clinics among 3591 individuals, 3.4% reacted to 2.0%, and 1.8% reacted to 1.0% (p < 0.001). A randomized double-blind repeated open application test performed in individuals reacting only to 2.0% but not to 1.0% showed that 9 of 17 formaldehyde-allergic individuals reacted to a moisturizer that contained formaldehyde (p < 0.001).
It is recommended that formaldehyde 2.0% aqua (0.60 mg/cm(2)) should replace formaldehyde 1.0% in the European baseline series from 2014. With the Finn Chamber(®) technique, a standardized amount of 15 µl of the solution obtained by using a micropipette should be used.