'The 73-year-old man looked up at the clear summer sky — the morning was nearly gone. He had finished mowing the main part of his lawn and was trimming the edges near the shrubbery with the weed wacker. He wanted to finish before the sun and heat made the work too hard. Suddenly he felt a sharp sting on the lower part of his shin. He glanced down at his bare leg. Nothing there. He still had the hedges to trim, so he kept working. He quickly finished the needed pruning, then moved on to the inside tasks he had planned.
It was late afternoon when the man called it a day and went to clean up before joining his family for dinner. Only in the shower did he take a good look at his leg. He found a distinct puncture mark where he had felt the sting, but it was just a dot — no big deal. Two days later, though, he noticed that the dot was now surrounded by a faint circle of red. He showed it to his wife, and she was concerned. She suggested he use an antibiotic ointment. She had some Neosporin on hand, and he applied it generously. Then he called to make an appointment with his doctor at the Hospital of St. Raphael’s Adult Primary Care Center in New Haven, Conn., just in case that wasn’t enough.
The next morning, he was glad he did. The circle of red was much bigger — about the size of a quarter — and a lot darker. And it was starting to hurt.
His usual doctor wasn’t available, so he had made his appointment with the advanced-practice nurse, Jana Young. She listened to the man’s story and his wife’s concerns as she looked at the red ring on his leg. It was slightly raised, with a clearing directly around the healing puncture site. When she touched the wound, it was tender, and the skin felt thickened and lumpy. There was no discharge, no crusting, no pus. It didn’t look like an infection. In fact, it didn’t look like anything she’d seen before. She brought in a colleague, an internist in the practice. He wasn’t sure what it was, either. . .
I had the man repeat his story. It offered me no new clues. I considered the possibilities. Lyme disease famously causes a bull’s-eye rash with a central clearing, but the time course was all wrong. . .
Keith Choate, a dermatologist, teaches residents with me at our clinic. This was one of his teaching days. Raman and I found the dermatologist trailed by a handful of residents. He wasn’t with a patient, and so we briefly described ours. We brought Choate into the patient’s room. The residents watched from the doorway. Choate introduced himself to the man, looked quickly at the twin rashes and asked just one question.
One Simple Question
“Are you using triple antibiotic ointment?” he asked the patient. Triple antibiotic ointment is a mixture of three topical antibiotics: neomycin, polymyxin B and bacitracin. It’s marketed under the brand name Neosporin, but generic versions of the mixture are available and sold under the name triple antibiotic ointment. The patient had been using this ointment, he told Choate. But only a few times, because it didn’t seem to help. “Well, don’t use it again,” Choate advised. The rash wasn’t an infection, helped by the topical antibiotic, but an allergy caused by it. This ointment is one of the most common causes of what is known as allergic contact dermatitis (A.C.D.).
The skin contains a wealth of white blood cells that help protect the body from invaders seeking to enter through this, the largest organ of the body. In allergic contact dermatitis, a benign substance that’s in touch with the skin is mistaken for a predator, triggering a protective inflammatory response. Some substances — including neomycin and bacitracin, two of the three antibiotics contained in this ointment — have been found to be frequent causes of this kind of mistaken protective reaction. According to one large study of surgical patients, more than 4 percent of those exposed to ingredients found in triple antibiotic ointment developed allergic contact dermatitis. It is frequently listed among the top 10 causes of A.C.D., along with some of the common ingredients in lotions and fragrances.
Choate recommended a strong steroid cream to help calm down the inflammation and speed resolution of the rash. But it will take time to clear up, the dermatologist warned.
Making Contact
As we left the room, Raman asked Choate how the rash spread to the other leg. His answer was simple and held a clue to how he figured it out. It’s a contact dermatitis, he reminded her. When the man crossed his ankles or put his legs next to each other, maybe as he slept, the ointment on one leg was put in contact with the other.
I spoke to the patient a week after he started the steroid cream. The rash was fading, but slowly. He’s been out to the spot in the yard where he felt the sting and searched the surrounding bushes and grasses for clues to what got him. He hasn’t found a likely culprit. No ant hills or beehives. No spearlike plants or grasses. No spider webs. It’s a mystery, he told me. But from now on, he averred, he’ll mow the lawn wearing long pants as well as socks and shoes.
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