Sahih Muslim 1201 c
The Book of Pilgrimage
It is permissible for a Muhrim to shave his head if there is a problem, but it is obligatory to offer a Fidyah for shaving it, and Clarifying what the Fidyah is
Kalb b. Ujra (Allah be pleased with him) reported: It was I for whom this verse was revealed (to the Prophet):" Whoever among you is sick or has an ail- ment of the head, he (may effect) a compensation by lasting or alms or a sacrifice" He said: I came to him (the Prophet) and he said: Come Dear. So I went near. He (again) said: Come near. So I went near. Thereupon the Messenger of Allah (ﷺ) said: Do the vermins trouble you? Ibn Aun (one of the narrators) said: I think he (Ka'b b. Ujra) replied in the affirmative. He (the Prophet) then commanded to do compensation by fasting or by giving sadaqa (feeding six needy persons) or by sacrifice (of a animal) that is available.