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To the Editor.—
I would like to amplify a few points raised by Willis and Kligman in their paper on "Photocontact Allergic Reactions" (Arch Derm100:535-539 [Nov] 1969).1. The authors are correct in stating that sometimes unbelievably small amounts of long ultraviolet are sufficient to elicit positive reactions in allergic photocontact dermatitis. As Willis and Kligman remark, their observations are based on experiments on prisoners who had been highly sensitized. But there are some patients with low degrees of photoallergic sensitivity who require much longer exposure to light. Sometimes even a half-hour exposure to natural sunlight or 20 minimal erythyma doses equivalent (MED equiv) from a filtered hot-mercury arc lamp may fail to elicit a reaction. I have observed cases where only very large amounts, say 60 MED equiv, or more, definitely proved the photoallergic sensitivity. Testing of such patients with larger amounts of light becomes important, if
Epstein S. PHOTOCONTACT ALLERGIC REACTIONS. Arch Dermatol. 1970;101(5):618-619. doi:10.1001/archderm.1970.04000050122021