In approximately 30% of cases of chronic diffuse loss of scalp hair with a duration of at least 6 months, no underlying abnormality can be found. Typically this occurs in women, starting abruptly without a recognizable initiating factor, and involving the entire scalp area with increased shedding of telogen hair. With the exception of bitemporal recession, hair thinning is usually discrete, and contrasts to the great emotional overtones in this situation. This may initially lead to the differential diagnosis of psychogenic pseudo effluvium. Due to synchronization of the hair cycle, the amount of shed hair is greater than that in androgenetic alopecia, while miniaturized hairs are not a feature of the disorder. Overlap with androgenetic alopecia and/or psychogeneic pseudo effluvium is not uncommon. Scalp dysesthesia or a sensation of "pain in the hair" (trichodynia) is an accompanying symptom in a significant proportion of cases, and correlates better with emotional upset than with actual hair loss. Current therapeutic recommendations are pragmatic, and based on both experimental observations of the sheep wool industry and clinical experience. They include the use of L-cystine-containing oral preparations and of corticosteroids. Further investigation into the molecular controls of the hair cycle are required to find a more specific form of therapy, for which the expense and risk-benefit ratio seem appropriate for the treatment of this benign condition.