This Was No Ordinary Sunburn. What Was Wrong?

“Come in out of the sun,” the woman shouted to her 80-year-old husband. “You’re turning red!” The man reluctantly trudged toward the house. It was late afternoon — the end of a glorious summer day in Orange, Conn. But when he glanced down at his exposed arms, he could see that she was right. He was a bright pink, and soon he knew his arms and probably the back of his neck would be red and itchy. It was time to go inside.

He suspected that it gave his wife kind of a kick for him to be suddenly as sensitive to the sun as she had always been. He loved the sun and until recently thought it loved him back, turning his olive skin a deep brown that seemed to him a signal of health. But that spring he started to get red wherever the sun hit him. It wasn’t exactly a sunburn, or at least not the kind of burn his wife used to get that made her skin turn red and peel and hurt for days.

His sunburn was itchy, not painful, and lasted an hour or two, sometimes a little more. It certainly never lasted long enough for his dermatologist, Dr. Jeffrey M. Cohen, to see it. He told his doctor about the rash that spring when he went in for his annual skin exam. Cohen said he might be allergic to the sun and suggested an antihistamine and a strong sunscreen. He took the pills when he thought of it and slathered on the sunscreen some of the time, but he wasn’t sure it did much. Besides, who ever heard of being allergic to the sun?

Clearly Not a Sunburn

He made an appointment with his dermatologist just before Christmas. It was one of those warm, sunny days in December, before winter really sets in, so he decided to make sure his doctor had a chance to see the rash. He arrived early and parked in the lot. He took off his jacket and stood in the sunshine that poured weakly over the building. After about 10 minutes he could see that he was getting pink, so he headed into the office.

“I’ve got something to show you,” he told Cohen with a smile when the doctor entered the brightly lit exam room. He unbuttoned his shirt to reveal his chest. It was now bright red. The only places on his torso that looked his normal color were those covered with a double layer of cloth — the placket strip beneath the shirt buttons, the points of his collar, the double folds of fabric over his shoulders. Palest of all was the area underneath his left breast pocket where his cellphone had been.

Cohen was amazed. This was clearly not a sunburn. To Cohen, it looked like a classic presentation of what’s called a photodermatitis — an inflammatory skin reaction triggered by sunlight. Most of these unusual rashes fall into one of two classes. The first is a phototoxic reaction, often seen with certain antibiotics such as tetracycline. When someone is taking these drugs, the sun can cause an immediate and painful sunburnlike rash that, like a regular sunburn, can last for days, causing blistering and even scarring. Clearly this patient had an immediate reaction to the sun, but he insisted his rash didn’t hurt. It just itched like crazy. And it was gone within hours. His reaction was more like a photoallergic dermatitis, in which sunlight causes hives — raised red patches that are intensely itchy and last less than 24 hours. But that didn’t quite fit either; photoallergic reactions aren’t immediate. They usually take one or two days to erupt after exposure to light.

Each reaction is triggered by medications. Cohen reviewed the patient’s extensive med list. Amlodipine, an antihypertensive drug, was known to cause this kind of photosensitivity, but the patient had started this medicine recently, months after he first mentioned the rash. Hydrochlorothiazide, another of his blood-pressure medicines, could sometimes do this. The patient had taken this drug for years and been fine, but at least in theory, this unusual type of reaction could start at any point.

Cohen explained his thinking to the patient. He would need to get a biopsy to confirm a diagnosis. The pathology would help him distinguish the inflammation of hives from the more destructive phototoxic reaction, which destroys the skin cells. And it would help him rule out other possibilities such as systemic Lupus erythematosus, an autoimmune disease that is most common in middle-aged women but can occur in men and women at any age.

A couple of days later, Cohen had his answer. It was hives — medically known as urticaria. This was a photoallergic reaction. And it was probably triggered by his hydrochlorothiazide. He should ask his primary-care doctor to stop the medication, Cohen told his patient, and after a few weeks he should stop getting the rash.

Through the Window

The man returned to Cohen’s office three months later. The rash was unchanged. After a few minutes in the sun he would be itchy and pink, even in the dead of winter. Cohen went back to the patient’s med list. None of the others had been linked to this type of reaction. “Tell me about this rash again,” he said. The patient went through his story once more. Any time sun hit his skin, even if the sun was coming through the window, he would turn red. When he was driving, the warm touch of the sun on his arm would cause an aggravating itch. And by the time he reached his destination that skin would be bright red. Hearing this description, Cohen suddenly realized he had it right the first time. The patient had developed an allergy to sunshine — a condition known as solar urticaria.

Cohen explained that this was not a sunburn. Sunburns are caused by light in shorter wavelengths known as ultraviolet B or UVB. That form of light cannot penetrate glass. The fact that he could get this reddening through his window indicated that his reaction was triggered by light with a longer wavelength, known as UVA. This is the form of light that causes skin to tan and to age, the form used in tanning salons.

Solar urticaria, he explained, is a rare disorder and not well understood. When sunshine penetrates the skin, it interacts in different ways with different cells. The most familiar are those cells that, when exposed, produce a pigment known as melanin, which tans the skin and offers some protection from other effects of the sun. In those with solar urticaria, the body develops an immediate allergic reaction to one of the cellular components changed by sunlight. How or why this change occurs is still not known. The allergy can start in young adulthood and may last a lifetime. And it’s hard to treat.

Sunscreen, Cohen told him, is a must — even when indoors. He would also need to take a higher dose of the antihistamine that he was prescribed — at least double the usual recommended dose. Patients are also advised to wear protective clothing. Solar urticaria can be dangerous. Extensive exposure to sunlight can trigger severe reactions and, rarely, a potentially lethal anaphylactic event.

The patient received the diagnosis just over a year ago and has been using sunscreen with an SPF of 50 ever since. He doubled the dose of his antihistamine. And most of the time, the medication plus long pants and sleeves and a hat keep him safe. Most of the time. And when he forgets, he knows he can count on his wife to let him know that he’s starting to turn red again.

Lisa Sanders, M.D., is a contributing writer for the magazine. Her latest book is “Diagnosis: Solving the Most Baffling Medical Mysteries.” If you have a solved case to share, write her at Lisa.Sandersmdnyt@gmail.com.