September 01, 2011
5 min read

Teenage girl, young boy present with edema, erythema and bullae in bizarre streaking pattern

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A teenage girl and her younger brother attended a Labor Day weekend barbecue with family in sunny San Diego. Bored out of their gourds, the two spent the day creating their own adventures — far away from the watchful eyes of their parents. The two started out by running a nature trail that wound its way from overgrown forest to manicured park and back again. Next, they cooled off with a quick dip in the ocean but decided the water was too choppy to stay in for long. They dried off and soon took matters into their own hands — literally — by starting a food fight with some fruit the adults had packed for their afternoon chilled beverages and snacks. The children stayed outside for the rest of the day to delay the inevitable return to school the next morning. The only apparent downside to the day was the “ice cream headaches” and stomachaches they developed after eating their dessert too quickly.

The next day, however, their return to school was made worse when the children’s mother noticed a strange rash with edema, erythema and bullae in a bizarre streaking pattern on both of the children. She waited about a week before bringing the children into your office because “the marks are starting to turn brown.” The children deny any pruritus but complain of mild tenderness on palpation.

What single question would most help get to the bottom of this mystery?

A.Were the two children playing in or around poison ivy, poison oak or poison sumac?

B.Were the children swimming in jellyfish-infested waters?

C.What specific fruits were they hurling at one another during that food fight?

D.Did the mother find a tick on any of the children?

Labor Day is upon us, and with it comes a rash of new cases of lime disease. The careful reader will note that I am not talking about Lyme disease, the most common tick-borne infection in North America. Instead, I am focusing on limes (Answer C), the little green fruit capable of sprucing up just about any food or drink.

That very same lime is also capable of causing a rash on any skin it touches. In fact, the same citrus fruit that once helped prevent scurvy in British sailors during the 19th century (hence the derogatory nickname “limey”) is also on the short list of usual suspects that cause a particular skin condition known as phytophotodermatitis.

Figure 1-2: The children’s mother noticed a strange rash with edema, erythema and bullae in a bizarre streaking pattern on both of the children.

Figure 2

Phytophotodermatitis is not just a triple-score Scrabble word. It is a reaction that occurs in skin exposed to sunlight or some other source of UVA radiation (320 nm to 400 nm) after contact with plants containing furocoumarins, a group of sensitizing substances found most commonly in plants of the family Apiaceae (eg, celery, fennel, parsnip, parsley, wild chervil, wild rhubarb, hogweed, false bishop’s weed, etc.). The family Rutaceae, which includes Key limes, lemons, grapefruit, burning bush, sweet and bitter oranges, and blister plants, make up the second most common source of phytophotodermatitis-causing plants. In particular, juice from the rind of the Persian lime, Citrus latifolia, constitutes a major cause of phototoxic reactions in the United States, especially in Florida and the Southwest desert. St. John’s wort (Hypericum perforatum), scurf-peas (Psoralea corylifolia), and the sap of fig trees (Ficus carica) are also known to contain furocoumarins in high concentration.

Serious reaction possible

People can acquire furocoumarins on their skin either directly (eg, by squeezing a lime) or indirectly (eg, small children affected through the “contaminated” hands of naive caretakers). Because this is not an immunologic response, no prior sensitization is necessary, and anyone can be affected. Although most reactions are mild, some can be quite serious. Reactions appear to depend both on the volume of furocoumarins that come in contact with the skin and the duration of exposure. Likewise, reactions are most commonly seen in mid to late summer, when furocoumarin concentrations are highest in the offending plants and when skin is more often exposed to direct sunlight. Wet skin, heat and sweating are known to exacerbate the phototoxic response.

The most severe furocoumarin reactions are associated with 5-methoxypsoralen (5-MOP) and 8-methoxypsoralen (8-MOP). Lime rinds, interestingly, contain 10 times the amount of 8-MOP than what is usually found in the pulp. In an oxygen-independent reaction, UVA radiation excites psoralens and forms covalent monoadducts with pyrimidines and interstrand crosslinks. Acute and direct damage to epidermal, dermal and endothelial cells occur when psoralens and oxygen interact to produce reactive oxygen species.

Figure 3-4: Phytophotodermatitis that occurred as a result of a food fight with limes.

Figure 4

Maximum cutaneous sensitivity to UVA peaks 30 minutes to 120 minutes after contact with furocoumarins. Within 24 hours to 72 hours, bizarre patterns of erythema, edema and bullae appear. Involved skin may remain hypersensitive to UV radiation for months to years. Notably, this painful, non-pruritic rash should only occur in sun-exposed areas.

Accompanying hyperpigmentation, which may be noted 1 to 2 weeks later and may last months to years, occurs as a combined result of increased tyrosinase activity, increased melanocyte mitosis and dendricity, melanocyte hypertrophy, and redistribution and increased size of melanosomes. Again, bizarrely shaped “drip” areas and “spritz” patterns have been documented, presumably after small drops of peel juice were sprayed onto the affected person’s skin. A less common reaction location is the upper lip, where furocoumarins reach the skin after a person comes into contact with the peel juice by, for example, biting or sucking the fruit directly.

Figure 5: The mother waited about a week before bringing the children into your office because “the marks are starting to turn brown.”

Phytophotodermatitis can be confused clinically with poison oak, poison ivy, poison sumac and chemical burns. It has been mistaken for child abuse when patients present with digitate hyperpigmentation as a result of being innocently touched by an adult with furocoumarins on their hands. Importantly, multiple hues are not seen in the skin lesions of phytophotodermatitis, as would be expected in healing bruises.

Look for other clues

Certain medical conditions (eg, lupus, porphyria, solar urticaria, etc.) and a number of medications (eg, doxycycline, hydrochlorothiazide, naproxen, amiodarone, etc.) can also predispose a person to light-sensitive reactions. Consequently, it is important to look for clues that help distinguish phytophotodermatitis from these other culprits.

Prompt evaluation by a physician is crucial because it allows: 1) timely patient education; 2) early treatment that can potentially decrease the amount of inflammation and subsequent skin darkening (usually with a short course of topical corticosteroids); and 3) consideration of other more serious conditions. Prevention, however, is the goal.

Bartenders and backyard barbecuers are not the only ones who need to be aware of phytophotodermatitis as a potential cause of a new rash on sun-exposed skin. Everyone with hobbies that put them in contact with furocoumarin-containing plants (especially hikers, florists, gardeners, agricultural workers and produce handlers) is at risk.

Physicians, as well, need to be on the lookout and must remember to keep an open mind and an open ear for clues that help “put the squeeze” on this summer diagnosis.

For more information:

  • Bolognia JL. Dermatology. 2nd ed. Philadelphia, Pa.: Elsevier; 2008: 249-252.
  • Goskowicz MO. Pediatrics. 1994;93:828-830.

Andrew C. Krakowski, MD, completed a residency in pediatrics at Johns Hopkins Medical Institute and a residency in dermatology at University of California, San Diego. He is currently a fellow in pediatric dermatology at Rady Children’s Hospital, San Diego. Catch him on Outdoor Channel as the host of boonDOCS Wilderness & Travel Medicine Show ( Disclosure: Dr. Krakowski reports no relevant financial disclosures.