Role of endogenous opioids in the effects of light on mood and behavior.

Skin cells produce endogenous opioids in response to light. This results in increased skin and plasma levels of endogenous opioids. Increased plasma levels of endogenous opioids may improve mood and affect behavior. The author suggests that improvement in mood after exposure to light may be related to the light-induced increase in levels of endogenous opioids. The author speculates that genetic factors may affect the response of skin cells to light: different people may have different genetically determined responses to natural or artificial light. The author also suggests that light may affect endogenous opioids via several different mechanisms.