Conditions and diagnosesExplainerMood and depression
Seasonal affective disorder: NIMH overview
Why depression that arrives with the dark months is a distinct pattern, and what the evidence actually says about light therapy.
National Institute of Mental Health6 min readSelected and edited by Dean ShabanAdded
NIMH's SAD page is careful about what is and is not known: the recurrent-winter pattern is well documented, the underlying mechanisms (circadian, serotonergic) are still being worked out, and bright-light therapy has reasonable evidence when used correctly.
Includes practical guidance on light boxes (intensity, timing, duration) that is often missing from consumer coverage.
Mental Hum's library is a curated index of authoritative third-party resources. The summary above is our own framing; the full information lives at the source.
A note on this article
Mental Hum publishes general education, not medical advice. If something here reflects your own experience, please consider speaking to a clinician. If you are in crisis, call or text 988.