“Get into the sun,” the woman yelled at her 80-year-old husband. “You’re blushing!” The man reluctantly steps towards the house. It was evening — the end of a glorious summer day in Orange, Conn. But when he looked down at his exposed arms, he saw that she was right. She was a bright pink, and soon she knew her arms and probably the back of her neck would be red and itchy. Time to go inside.
He suspected that this gave his wife some sort of kick for him to suddenly be as sensitive to the sun as before. He loves the sun and until recently thought it loved him back, turning his olive skin a deep brown which seemed to him a sign of health. But that spring he began to turn red wherever the sun hit him. It wasn’t exactly a sunburn, or at least not the kind of burn her husband got that caused her skin to turn red and peel and hurt for days.
His sunburn was itchy, painless, and lasted an hour or two, sometimes less. It certainly didn’t last long enough for her dermatologist, Dr. Jeffrey M. Cohen. She told her doctor about the rash last spring when she went in for her annual skin exam. Cohen said she might be allergic to the sun and suggested an antihistamine and a strong sunscreen. He took pills when he thought about it and sometimes slathered on sunscreen, but he wasn’t sure it did much. Also, who ever heard of being allergic to the sun?
Definitely Not Sunburn
She made an appointment with her dermatologist before Christmas. It was one of those warm, sunny days in December, before winter set 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 sunlight that poured gently into the building. After about 10 minutes she saw that she was turning pink, so she went to the office.
“I’ll show you something,” he smiled at Cohen as the doctor entered the bright exam room. He unbuttoned his t-shirt to reveal his chest. It is bright red now. The only places on his body that looked normal in color were the ones covered by the double layer of fabric — the placket strip under the shirt buttons, the points of his collar, the double folds of fabric on his shoulders . The whitest of all is the area under his left breast pocket where his cell phone is kept.
Cohen was surprised. This is clearly not a sunburn. To Cohen, it sounded like a classic presentation of what’s called 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 a person takes these medications, the sun can cause an immediate and painful sunburn-like rash that, like a regular sunburn, can last for days, causing blistering. and even scarring. This patient clearly had an immediate reaction to the sun, but she insisted that her rash was not painful. It just itches like crazy. And it was gone in a few hours. Her reaction is more like a photoallergic dermatitis, where sunlight causes rashes – raised red spots that are very itchy and last less than 24 hours. But that didn’t quite fit; photoallergic reactions are not immediate. Eruption usually takes a day or two after exposure to light.
Each reaction is triggered by drugs. Cohen reviewed the patient’s extensive med list. Amlodipine, an antihypertensive drug, is known to cause this type of photosensitivity, but the patient started this drug recently, several months after he first mentioned the rash. Hydrochlorothiazide, another of his blood pressure medications, can sometimes do this. The patient has been taking this drug for years and has been doing well, but at least in theory, this unusual type of reaction can start at any point.
Cohen explained his thinking to the patient. He will need a biopsy to confirm the diagnosis. Pathology will help him distinguish the inflammation of the hives from the more destructive phototoxic reaction, which destroys skin cells. And it can help her rule out other possibilities like systemic Lupus erythematosus, an autoimmune disease most common in middle-aged women but can occur in men and women of any age.
A few days later, Cohen got his answer. It’s a rash — medically known as urticaria. This is a photoallergic reaction. And his hydrochlorothiazide probably triggered it. She should ask her primary care doctor to stop the medication, Cohen told her patient, and after a few weeks she should stop having the rash.
At the window
The man returned to Cohen’s office three months later. The rash does not change. After a few minutes in the sun he will be itchy and pink, even in the dead of winter. Cohen went back to the patient’s med list. None of the others have been linked to this type of reaction. “Tell me about this rash again,” he said. The patient goes through his story again. Anytime the sun hit her skin, even if the sun came through a window, she would turn red. When he was driving, the hot touch of the sun on his arm would cause severe itching. And by the time he reached his destination that skin was bright red. Hearing this description, Cohen suddenly realized that he was right the first time. The patient developed an allergy to sunlight – a condition known as solar urticaria.
Cohen explains that it’s not sunburn. Sunburns are caused by light at shorter wavelengths known as ultraviolet B or UVB. That form of light cannot penetrate glass. The fact that he could get the redness on 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 wrinkling and aging, the form used in tanning salons.
Solar urticaria, he explained, is a rare disease and not well understood. When sunlight penetrates the skin, it interacts in different ways with different cells. The most familiar are cells that, when exposed, produce a pigment known as melanin, which darkens the skin and offers some protection from the sun’s other effects. In those with solar urticaria, the body develops an immediate allergic reaction to one of the cellular components that is altered by sunlight. How or why this change occurs is still unknown. Allergies can start in young adulthood and can last a lifetime. And it’s hard to treat.
Sunscreen, Cohen told him, is a must — even indoors. He will also need to take a higher dose of the antihistamine he is 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 fatal 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 usually, medicine along with long pants and sleeves and a hat keeps him safe. Most of the time. And when she forgets, she knows she can count on her husband to let her know that she’s starting to blush again.
Lisa Sanders, MD, is a contributing writer for the magazine. His most recent book is “Diagnosis: Solving the Most Baffling Medical Mysteries.” If you have a solved case to share, write to her at Lisa.Sandersmdnyt@gmail.com.