Nocturnal clitoral tumescence (NCT), colloquially known as morning bean, is a spontaneous
swelling of the clitoris during sleep or when waking up. Similar to the process in males,
nocturnal penile tumescence
Nocturnal penile tumescence (NPT) is a spontaneous erection of the penis during sleep or when waking up. Along with nocturnal clitoral tumescence, it is also known as sleep-related erection. Colloquially, the term morning wood, or less commonly, ...
, females experience clitoris tumescence and engorgement of the vagina, mainly during the
REM sleep
Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals (including humans) and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the s ...
phase.
According to Fisher et al., the increase in vaginal blood flow associated with NCT during REM sleep is similar to the process in men in frequency, i.e. 95% of REM phases. 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. The erection may be associated with erotic dreams and even, occasionally,
sleep orgasms.
The phenomenon was first documented in 1970 by Karacan et al., with a single aforementioned follow-up study in 1983 by Fisher et al.
[ 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. The study did not measure specific sleep phases. Increases in vaginal pH are associated with sexual arousal and clitoral erection. ]Bartholin's glands
The Bartholin's glands (named after Caspar Bartholin the Younger; also called Bartholin glands or greater vestibular glands) are two pea-sized compound alveolar glandsManual of Obstetrics. (3rd ed.). Elsevier. pp. 1-16. . located slightly posteri ...
secrete alkaline fluid to lubricate the vagina during arousal, increasing vaginal pH.
See also
* Rapid eye movement sleep
Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals (including humans) and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the s ...
References
Sleep
Clitoris
Sexual arousal
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