Painful sunburn-like rash after beach holiday in a young woman on acne treatment

A 25-year-old woman presented to the dermatology clinic with a painful rash on her face, upper chest, and arms. She had returned from a beach holiday five days earlier. She had spent the holiday sunbathing and said she had used sunscreen, but not always reapplied it. The rash began on the third day of the holiday, as a burning erythema on the exposed areas, which then became swollen and tender. She described it as 'like a bad sunburn but worse'. On examination, there were well-demarcated erythematous patches with oedema on the forehead, cheeks, the V of the neck, dorsal forearms, and the anterior shins. The skin in these areas was warm and tender to touch. There were no blisters. The rash spared sites covered by clothing. She had no fever, no mucosal lesions, and no photosensitivity to artificial light. Her medication history was as follows: she had been taking doxycycline 100 mg once daily for acne vulgaris for the previous three months. She had also been taking a combined oral contraceptive pill (ethinylestradiol 30 micrograms/levonorgestrel 150 micrograms) for the previous six months. She had not started any other new medications recently. She had no known drug allergies. She did not use any topical medications on the sun-exposed areas. Investigations: full blood count, liver function tests, and renal function were normal. Antinuclear antibody and anti-Ro/anti-La antibodies were negative. A punch biopsy from a lesion on the arm showed a superficial perivascular lymphocytic infiltrate with occasional eosinophils, consistent with a phototoxic drug eruption. The rash improved after stopping doxycycline, with complete resolution over two weeks. She was not rechallenged with the drug. She was advised to continue to avoid sun exposure and to use broad-spectrum sunscreen. On follow-up, she had no recurrence. Her acne was subsequently managed with topical adapalene.