Appears in
On Food and Cooking

By Harold McGee

Published 2004

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Psoralens are chemicals that damage DNA and cause blistering skin inflammations. They’re found occasionally in badly handled celery and celery root, parsley, and parsnips, when these vegetables have been stressed by near-freezing temperatures, intense light, or infection by mold. Psoralens are absorbed through the skin during handling, or by being ingested with the vegetable, either raw or cooked. They lie dormant in skin cells until they’re struck by ultraviolet rays in sunlight, which causes them to bind to and damage DNA and important cell proteins. The psoralen-generating vegetables should be bought as fresh as possible and used quickly.