Unusual Skin Reaction to Sunlight: A Comprehensive Guide by Dr. Xiao Weijun

2023-09-01 07:03:47

The olive skin turned dark brown, which might seem like a sign of health to a person, but that spring, the sunlit areas began to turn red. It wasn’t exactly a sunburn, but it wasn’t like the kind of burns I’d experienced before that left my skin red, flaky, and painful for days. Red and itchy skin? Is this a normal sunburn?Doctor Xiao Weijun column

Red and itchy skin? Is this a normal sunburn?Doctor Xiao Weijun column

Apparently it’s not a sunburn – Physician Xiao Weijun’s column

The patient showed bright red skin, and the only places on the torso that appeared to be of normal color were those covered by a double layer of fabric—the placket under the buttons of the shirt, the collar point, the double folds of the fabric over the shoulders. This was clearly not a sunburn, and to doctors it looked like a classic sign of what’s known as photodermatitis, an inflammatory skin reaction triggered by sunlight.

Most of these unusual rashes fall into one of two categories. The first is a phototoxic reaction, common with certain antibiotics (such as tetracyclines), when someone takes these drugs, the sun immediately causes a painful sunburn-like rash that, like a normal sunburn, can last for days , leading to blisters and even scarring.

Almost every reaction was triggered by a drug, consulted the patient’s detailed drug list, Amlodipine is an antihypertensive drug known to cause this photosensitivity, but the patient had recently started taking it , months after he first mentioned the rash. His other blood pressure drug, Hydrochlorothiazide, sometimes does that too. The patient had been taking the drug for years and was doing well, but the unusual reaction could have started at any time, at least in theory.

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At this point a biopsy is needed to confirm the diagnosis, and pathology will help differentiate urticarial inflammation from a more destructive phototoxic reaction that destroys skin cells. The process was ruling out other possibilities, such as systemic lupus erythematosus, an autoimmune disease that most commonly affects middle-aged women but can of course occur in men and women of any age.

Solar urticaria

A few days later, we got the answer, medically known as hives. It was a photosensitivity reaction, most likely triggered by his Hydrochlorothiazide. Advise patients not to use the drug because of allergic reactions.

This is not a sunburn, sunburn is caused by a shorter wavelength of light called ultraviolet B or UVB, basically this form of light cannot penetrate glass. But the patient could see this reddening through a window, suggesting his reaction was triggered by longer-wavelength light called UVA, the form of light that causes skin to tan and age.

Solar urticaria is a rare condition that we don’t understand well enough in current medicine that when sunlight penetrates the skin, it interacts with different cells in different ways. The most common are those cells that, when exposed, produce a pigment called melanin, which gives the skin a tan and provides some protection from the sun’s other effects.

In people with solar urticaria, the body has an immediate allergic reaction to a cellular component that sunlight changes. How or why this change occurs remains unclear. Allergies can start in early adulthood and can last a lifetime, and are difficult to treat.

Extended reading of Dr. Xiao Weijun’s column:

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Diagnosis and Treatment – Doctor Xiao Weijun Column

Sunscreen is a must – even indoors. Higher doses of antihistamines, at least twice the usually recommended dose, are also required. Patients are also advised to wear protective clothing. Solar urticaria can be dangerous. Large exposures to sunlight can trigger severe reactions and, in rare cases, potentially fatal anaphylaxis.

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