Phyto What?

By Peter Galvin, MD

This case comes from the Mike O’Callaghan Military Medical Center at Nellis Air Force Base in Nevada. A 40-year-old man presented to the allergy clinic with a two-day history of a burning rash on both hands. One day before the development of the rash, he had manually juiced 12 limes and then attended an outdoor soccer game. He had not used sunscreen. Physical examination was notable for a confluent area of erythema (redness) extending from his thumbs to the middle of his second finger. There were scattered patches of erythema on his knuckles and other fingers and a small blister was noted at the base of his left thumb (see Panel A). It was also noted that part of his left fourth finger was covered by a wide ring, and the skin under the ring was not affected (see Panel B). A diagnosis of phytophotodermatitis was made.

Phytophotodermatitis is a phototoxic skin reaction that results from exposure to furocoumarins – a plant substance (phytochemical) found in limes, lemons, celery, carrots, and parsley – and ultraviolet light. These chemicals protect plants from predators like insects, mammals, and fungi. When a person handles these plants, furocoumarins are absorbed into the skin. Exposure to ultraviolet light causes the chemicals to bind to cellular DNA causing cell death and local inflammation. Exposure to heat and moisture may also activate the chemicals. The effects of phytophotodermatitis may be severe, with erythema, edema (swelling), blisters, and itching. Over time they may also cause hyperpigmentation or darkening of the skin. Interestingly, in figs it is the leaves, not the fruit, that contains furocoumarins. This fact was known by Egyptians as far back as 2000 B.C., who used the milky sap of fig leaves to treat people with vitiligo (patchy depigmentation of the skin). They would apply the milky sap from fig leaves to pale patches of skin and then tell the patient to go and lie in the sun.

Furocoumarins are also responsible for the “grapefruit juice effect” in which blood levels of certain drugs may be markedly altered by simultaneous ingestion of grapefruit juice and medication. In children, phytophotodermatitis may be mistaken for child abuse. The way to avoid a skin reaction after handling these plants is to wash your hands in soap and cold water and wear sunscreen if you must be in the sun. The patient in this case was treated with topical steroid cream and his skin returned to normal after several months.

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