Q: What is the ruling on combing hair gently for a male Muhrim (pilgrim in the ritual state for Hajj and ‘Umrah)? Is it forbidden?
A: A male Muhrim should not comb his hair. If he scratches his head or skin gently, this is not a problem, but it is not permissible for a man in Ihram to comb his hair in such a way that some of it is cut, or to cut his nails or skin. That is because once a Muslim man assumes Ihram, he should not cut his hair or nails, wear perfume, cover his head with a turban or anything similar, cover his body with a Qamis (long shirt) or other sewn clothing, or kill the game - all these acts are not permissible for a male Muhrim. He should also not conclude a marriage contract, offer marriage to a woman, or contract a marriage for his female relative while in Ihram. Conjugal intercourse, touching and kissing one’s spouse, and the like, are also forbidden until major Tahalul (final removal of the ritual state for Hajj and ‘Umrah). All these things are forbidden to do after assuming Ihram.
[Fataawa Shaykh Ibn Baaz]