Clinical Image: Phytophotodermatitis: A butterfly‐like rash on the face of a young woman

The patient, a 35‐year‐old woman, presented to our clinic with erythema and swelling of her face for 3 days. Three days ago, she had about 400 g of celery root for lunch. Then she spent the rest of the day working on a farm under the sun without using sunscreen. Several hours later, she noted mild erythema with a sting on her cheeks. Then her condition progressed to intense skin redness with apparent edema. A physical examination revealed dusky red erythema and petechiae on the swelling malar region. Unexposed skin and other sun‐exposed areas, including the lateral face as well as her arms and hands, which were covered by her long wrap, long‐sleeved blouse, and gloves, were spared. The patient denied taking medications and denied a history of contact dermatitis or similar reactions. There was no family history of autoimmune disease. Laboratory test results for complete blood cell count, urinalysis, antinuclear antibody, and other serum autoantibodies were unremarkable. The diagnosis of celery‐related phytophotodermatitis was made. After wet dressing and supportive treatments, complete resolution was observed within 2 weeks. Phytophotodermatitis is a phototoxic reaction triggered by photosensitizing substances (1). Psoralen is one common photosensitizing substance in plants. After exposure to ultraviolet A (UVA) radiation, psoralens cross‐link with pyrimidine bases on the DNA in keratinocytes, and phytophotodermatitis develops. An early study reported that 0.5 mg of psoralen could be extracted from 10 g of celery root (2). The 400 g of celery root contained 20 mg of psoralen, which is enough to lower the UVA‐induced erythema threshold in specific individuals under certain circumstances. Phytophotodermatitis can mimic other photoinduced or photoexacerbated conditions, including lupus erythematosus, sunburn, and contact dermatitis. The final diagnosis could be made according to the medical history, especially with inquiry about plant or plant extract contact, clinical manifestation, and laboratory test results. A skin biopsy may help clinicians reach a diagnosis for patients without improvement after treatment, which primarily involves cool compresses, emollients, and topical steroids.

This work was supported by the National Nature Science Foundation of China (81703148, 81472905).