An 80-year-old man used to love to bask in the sun, but recently, he began to get red and itchy wherever the sun hit him, even if it was only for a short amount of time. His doctor said what he was experiencing was "clearly not a sunburn" and that another, rarer condition was likely the culprit, Lisa Sanders writes for the New York Times Magazine.

A short, itchy sunburn

An 80-year-old man loved being in the sun, but one spring, he started to get red wherever the sun would hit his skin.

However, "[i]t 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," Sanders writes. Rather than being painful, the man's sunburn was itchy and typically only lasted a few hours a most.

When the man told his dermatologist Jeffrey Cohen about the rash during an annual skin exam, Cohen said he might be allergic to the sun. Cohen suggested the man use an antihistamine and strong sunscreen.

Could medications be triggering the patient's rash?

Although the man took the antihistamines and used the sunscreen some of the time, he wasn't sure if they had much effect. Just before Christmas, the man made another appointment to see Cohen. Before going inside the office, the man stood in the sunshine for around 10 minutes so he could show Cohen his rash.

Once in the exam room, the man unbuttoned his shirt to reveal his chest, which was now bright red. The only places on his chest that were a normal color were those that had been covered by a double layer of cloth from his shirt.

"Cohen was amazed," Sanders writes. "This was clearly not a sunburn." According to Cohen, the patient's redness seemed like a classic presentation of photodermatitis, or an inflammatory skin reaction caused by sunlight.

This condition typically falls into two categories: a phototoxic reaction or a photoallergic dermatitis. Phototoxic reactions are also caused by certain antibiotics, such as tetracycline. When taking these drugs, the sun can cause an immediate and painful sunburn-like rase, which can last for days.

In comparison, photoallergic dermatitis can lead to hives, which are intensely itchy red patches that last less than 24 hours, after being in the sun. However, photoallergic reactions typically take one or two days to appear after sunlight exposure.

Although neither reaction exactly fit the patient's rash, which was immediate and itchy but not painful, Cohen reviewed his extensive medication list. Some of the medications the patient was taking, such as amlodipine and hydrochlorothiazide, could potentially cause his reactions, but Cohen said he would need to get a biopsy to confirm his diagnosis, as well as rule out other potential conditions, such as Lupus erythematosus.

A few days later, the biopsy confirmed that the patient was experiencing hives and had a photoallergic reaction to the sun. Cohen determined that the likely culprit was the hydrochlorothiazide the patient was taking. He recommended the patient ask his primary care doctor to stop the medication so that the patient would stop getting the rash in a few weeks.

'He had it right the first time'

Three months later, the patient made another appointment with Cohen, saying that his rash had remained unchanged. Even a few minutes in the sun would cause his skin to become pink and itchy.

Although Cohen reviewed the patient's medication list again, none of other medications had been linked to this kind of reaction. "Tell me about this rash again," Cohen said.

This time, the patient explained that any time sunlight hit his skin, even if it was coming through a window, he would turn red. After "[h]earing this description, Cohen suddenly realized he had it right the first time," Sanders write.

Like Cohen had originally suspected, the patient had developed an allergy to sunlight, a condition known as solar urticaria. The fact that the patient was getting a rash even from sunlight through his window meant that the reaction was triggered by longer wavelengths of light known as ultraviolent A or UVA rays. UVA rays cause skin to tan and age, while sunburns are caused by shorter UVB rays.

According to Cohen, solar urticaria is a rare disorder in which the body has an immediate allergic reaction to a cellular component affected by sunlight. How or why this reaction occurs is unknown, and it is often difficult to treat.

Going forward, Cohen told the patient that he should use sunscreen, even while indoors. He should also take at a higher dose of an antihistamine and wear protective clothing when outside since solar urticaria can be dangerous and lead to severe reactions.

Since receiving the diagnosis, the patient has been using a sunscreen with an SPF of 50 and has doubled his antihistamine dose. "[M]ost of the time, the medication plus long pants and sleeves and a hat keep him safe," Sanders writes. But "when he forgets, he knows he can count on his wife to let him know that he's starting to turn red again." (Sanders, New York Times Magazine, 7/8)