A 37-year-old Japanese man presented with alopecia after being involved in a traffic accident. An immunohistochemical study of the biopsy specimen demonstrated that CD8⁺ T cells infiltrated into hair follicles with satellite cell necrosis of keratinocytes. Four weeks after his initial visit, he again had another traffic accident. Despite the treatment with oral prednisolone and a topical steroid, the alopecia became universalis. Treatment with systemic and topical steroids was continued, and 12 weeks later, white vellus hairs grew over the whole scalp. Intracytoplasmic study revealed that there was a positive correlation between the severity of the alopecia and the increase of interferon-γ producing Th1 cells or interleukin (IL)-17 producing Th17 cells, whereas the number of IL-4 expressing Th2 cells was inversely proportional to the extent of alopecia. The autoimmune hair loss might occur via the activation of T helper 1 (Th1) and Th17 cells.