Relationship between formaldehyde and quaternium-15 contact allergy. Influence of strength of patch test reactions.

BACKGROUND In groups of patients with formaldehyde allergy, many have positive patch tests to quaternium-15. Conversely, of patients allergic to quaternium-15, over half also react to formaldehyde. OBJECTIVES To test our hypothesis that patients with stronger patch test reactions to formaldehyde are more likely to react to quaternium-15, attesting to the aetiological role for formaldehyde in such co-reactivity. METHODS Retrospective analysis of all patients patch tested with formaldehyde and quaternium-15 in the European baseline series between 1994 and 2009 (TRUE test). RESULTS In a group of 86 patients allergic to formaldehyde, 73% co-reacted to quaternium-15; in the subgroup of 70 women, the percentage was 83. In both groups, more reactions were observed to quaternium-15 in the patients with a ++ reaction compared to the patients with a + reaction to formaldehyde. Conversely, stronger reactions to quaternium-15 were significantly more often associated with formaldehyde sensitivity in a group of 107 patients reacting to quaternium-15 and a subgroup of 88 women. In men, such effects were not observed and only 5 of 16 (31%) men allergic to formaldehyde also reacted to quaternium-15. CONCLUSIONS In women, but not in men, stronger reactions to formaldehyde lead to more positive quaternium-15 patch tests.