Canities subita, also called Marie Antoinette syndrome or Thomas More syndrome, is an alleged condition of hair turning white overnight due to stress or trauma. The trivial names come from specific cases in history including that of Queen Marie Antoinette of France whose hair was noted as having turned stark white overnight after her capture following the ill-fated flight to Varennes during the French Revolution. An older case of Sir Thomas More's hair turning white the night before his beheading has also been recorded. Although a number of cases of rapid hair greying have been documented, the underlying patho-physiological changes have not been sufficiently studied.
The syndrome has been hypothesized to be a variant of alopecia areata diffusa or autoimmune non-scarring hair loss that selectively affects all pigmented hairs, leaving only the white hair behind. Marie Antoinette syndrome is caused by high levels of emotional stress, which, in turn, causes less pigmenta