Celery contains psoralens, a compounds that can increase a person’s skin sensitivity to ultraviolet light. According to a October 2000 article in the “Baylor University Medical Center Proceedings,” if a person were to put celery juice on their skin and subsequently go out into the sun, the skin in that area will develop a type of burning dermatitis or rash within 12 to 36 hours.
Sources:
https://www.ewg.org/foodnews/summary.php
https://ndb.nal.usda.gov/ndb/foods/show/2962?fg=&man=&lfacet=&format=&count=&max=25&offset=&sort=&qlookup=celery
https://www.epa.gov/pesticides
