The case of the mysterious blisters

Sea & Shore, Summer, 2009 by Laura Mussulman

The Midwest was having another summer heat wave, so I didn't hesitate when a friend invited my daughter and me to spend a day boating with her. I jumped at the chance to explore Smithville Lake in Kansas City, Mo.

The sun was intense, with temperatures in the mid-90s. Being the conscientious parent I am, I insisted my daughter wear her life jacket the entire time we were on the lake. I also applied lots of SPF-50 sunscreen to her fair skin. However, I wasn't as conscientious about my own fair skin--I only used an SPF-8 sunscreen.

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By midday, we were ready for lunch, so we anchored the boat in a cove, and my friend offered me a Corona with fresh lime. "That'll be the perfect choice to quench my thirst," I thought. I squirted the lime in my beer and wiped off the excess juice dripping dripping down my right hand onto my right thigh.

After lunch, my 2-year-old daughter pretended to drive the boat and played in a big inner tube, while my friend and I swam in the lake. We spent the entire day on the water, and by late afternoon, I could tell I had gotten too much sun.

I awoke Sunday morning to find my shoulders and legs were pink--not the worst sunburn I've ever had but bad enough. By Monday morning, I began to notice my right thigh had five red streaks, and my sunburn seemed more intense. As the day passed, the streaks turned into a 2nd-degree burn and began to blister. My right thigh looked like I had laid a hot curling iron on it five times. Meanwhile, my left thigh had a couple of thin, long, dark streaks and one large blister. I also discovered my stomach had a small, splattered pattern of blisters.

By Monday night, I was beginning to wonder what could have caused such an intense burn; the blisters were nickel size and quarter-inch thick. I looked through an old dermatology book from college for something to explain such a mysterious reaction, but I didn't find anything.

Because I work at a medical hospital, I consulted with two physician friends on Tuesday morning, and they said I definitely had a 2nd-degree burn from the sun. I wasn't convinced, however, that the sun alone could have caused such intense burning in this peculiar pattern. Other parts of my body that were more sunburned didn't have the same reaction.

By mid-afternoon, I was limping from the intense pain. A co-worker asked me what was wrong and, after taking one look at my burn pattern, immediately asked if I had had limes while on the boat. Her question took me by surprise, but I acknowledged I had squirted some lime in my drink. Unfortunately, some of the initial squirt had gone on my stomach--I had worn a bikini that day--and I also remembered wiping my right hand on my right thigh afterward.

The co-worker then told me about a friend of hers who had experienced the same thing once at the beach. The beach medics who treated her knew the burn was caused by lime juice, in combination with the intense sun exposure. The clinical name for the condition is phytophotodermatitis (PPD), sometimes called phototoxic dermatitis [see inset photo on previous page]. The clinical pattern is that the blisters don't develop until 24 to 72 hours after exposure, just as mine had done.

I investigated further and found that key clues to diagnosing PPD include "bizarre inflammatory patterns and linear streaks of hyperpigmentation. These patterns often result from brushing against a plant's stems or leaves while outdoors or from the liquid spread of lime juice over the hand or down the forearm. A handprint pattern from lime-juice contact is not uncommon."

Although the burn is extremely painful, it was interesting to solve this puzzling mystery. My advice is to be careful this summer, and always wear sun block. More importantly, always wash off any lime juice while you're at the pool, lake or beach.

By LCdr. Laura Mussulman

NOSC Kansas City

The author is a Navy Reserve aerospace physiologist who was on AcDuTra at the Naval Safety Center when she wrote this article.