A teen’s strange rash has her dad wondering about a ‘shopping allergy’ | Medical Mystery

A 16-year-old girl went to her longtime primary care doctor after dealing with a rash that had bothered her off and on for about two months. This itchy, red, and inflamed rash usually turned up on her neck, upper back, and buttocks.

Skin issues were not new to the teen; when she was younger, she had atopic dermatitis (eczema) and for the previous three months she was on an oral antibiotic (doxycycline) for acne. The doctor asked about other symptoms and the patient said she had been feeling tired lately, and for the past two days her right knee had been hurting. On examination the rash was red, dry, and bumpy, and was on her neck, waist, upper thighs, and buttocks. Her right knee was also slightly tender.

Common things are common in medicine, so the doctor considered the possibility of a “viral exanthem,” or rash caused by a viral illness. The teen had been feeling tired lately but had not had any respiratory or gastrointestinal symptoms to suggest a viral infection. Plus, rashes with viruses are generally more widespread than what this patient was experiencing.

The doctor learned that the teen was up late using her phone and laptop, and getting only 5 hours of sleep a night, explaining her fatigue. It would be wise, the doctor counseled, to get the recommended 8-10 hours of sleep a night.

Rheumatologic illnesses, like lupus, can cause rashes and joint problems, such as the sore knee this patient complained of. But she did not have any fevers or swelling, stiffness or redness of the joints, and there was no family history of rheumatologic diseases, making this diagnosis less likely.

The doctor knew the patient was a competitive cheerleader, and asked her how that was going. Turns out she twisted her knee on a landing, explaining the knee pain.

Next on the list of considerations was the doxycycline, which can increase sensitivity to the sun, leading to rashes in sun-exposed areas. The teen was in Florida for a week with the cheer team for winter break, but said she consistently used broad spectrum, water-resistant, SPF30 or higher sunscreen diligently re-applied every 2 hours and after swimming. Also, the rash was not in areas exposed to the sun, so it was not the doxycycline.

Was this just the patient’s eczema? When she was younger, she had eczema on her ears, hands, and the inside of her elbows and knees, but the location of her current rash was much different. The PCP asked about other possible triggers for the rash, but the patient had not changed any of her soaps or laundry detergent.

The only change she mentioned was, because it was frigid outside, she and her friends were going to the mall a lot where they tried on trendy clothes including chunky sweaters, distressed jeans, and formal dresses. Her father joked, “She must be allergic to shopping!” The teen found this less amusing than her father did.

The PCP explained to the patient and her father that this was most likely allergic contact dermatitis, which is a delayed allergic reaction that usually occurs 48-72 hours after exposure to an allergen. It is caused by the skin ramping up an immune response against a triggering substance that contacts the skin. The doctor suspected that the patient may be allergic to the chemical additives in the clothing, like dyes or antiwrinkle agents. People with conditions that affect their skin barrier, like eczema, are more prone to having allergic contact dermatitis.

The doctor counseled the patient to wash new clothes before wearing them, and to wear loose fitting garments to minimize the rubbing on her skin. She recommended using a moisturizer and prescribed her a topical steroid for the most severe areas. She referred the patient to a dermatologist to help identify exactly what the patient might be reacting to, so she could, among other things, more safely navigate future shopping trips.

The patient was thrilled that she was not, in fact, allergic to shopping, triumphantly telling her father: “I told you so!”

Samantha Starkey is a pediatric resident and Rima Himelstein is an adolescent medicine specialist at Nemours Children’s Health, Delaware.