Nocturnal clitoral tumescence (NCT), colloquially known as morning bean,[1] is a spontaneous swelling of the clitoris during sleep or when waking up.
It does occur a bit more often in non-REM sleep, and each episode appears shorter in duration.
In terms of size, NCT is similar to that induced by erotic stimulation when awake.
[3] The phenomenon was first documented in 1970 by Karacan et al.,[4] with a single aforementioned follow-up study in 1983 by Fisher et al.[3] More recent research includes a 2023 study by Gören et al., who found that their subjects displayed vaginal pH changes at different periods throughout the night.
Bartholin's glands secrete alkaline fluid to lubricate the vagina during arousal, increasing vaginal pH.