Background: In Japan, a considerable number of adult patients with atopic dermatitis suffer from recalcitrant facial erythema that resists common treatment with topical corticosteroids and antihistamines. Objective: Our purpose was to investigate the potential role of sun exposure in the aggravation of these facial lesions. Methods: The history of photoaggravation was taken from 74 adult patients with atopic dermatitis who suffered from recalcitrant facial erythema. Repeated UVB and UVA phototests were performed in 36 patients. Surface markers of infiltrating cells in UVB-provoked lesions were characterized immunohistochemically. Results: Forty-one of 74 patients experienced an exacerbation of the facial lesions after sun exposure. UVB testing revealed an abnormal, papular response in 14 of 36 patients. All of the 14 patients complained of clinical aggravation after sun exposure. No abnormal reactions were observed at UVA testing. In UVB-provoked lesions, CD4+ cells were predominant to CD8+ cells. Conclusion: Exposure to UVB radiation may be responsible for the recalcitrant facial erythema in at least some of the patients with atopic dermatitis.