expression, godan verb (-su)
surrender one's chastity to a man; give oneself to a man
A euphemistic expression for a woman consenting to sexual relations with a man, often implying a first time or a significant emotional step.
彼女はついに彼に肌を許した。
She finally surrendered her chastity to him.
身を任せる is a broader phrase meaning 'to entrust oneself' or 'to give oneself over' to a situation or person, not specifically sexual. 肌を許す is specifically about a woman consenting to sex.
The expression combines 肌 (skin, body) with 許す (to permit, to allow), literally 'to allow one's skin/body', a euphemism for granting sexual access.