פירוש על ויקרא 21:5

לא יקרחו קרחה THEY SHALL NOT MAKE BALDNESS [UPON THEIR HEAD] for the dead. But were not the ordinary Israelites also forbidden in respect of this? Why then is this law especially stated with reference to the priests? But because in the prohibition addressed to the ordinary Israelites it is stated, (Deuteronomy 14:1) “[Ye shall not make anybaldness] between your eyes [for the dead]”, I might think that one is not liable to punishment for making baldness on any other part of the whole head, Scripture therefore states here: “upon their heads”; and now that we have both commands, the law regarding the Israelites may be derived from that addressed to the priests from a similarity of terms used in both prohibitions: the term “קרחה” is used here, and in the prohibition regarding the Israelites it also uses the term “קרחה”; what is the case here? The prohibition applies to the whole head! So, also, there the whole head is included in the prohibition. And, on the other hand, how is the case there? The prohibition is limited to making baldness for the dead! So here too it applies only to such baldness as is made for the dead (Makkot 20a; Kiddushin 36a).

לא יקרחו, even though I have permitted the priests to defile themselves to bury their close relatives and express mourning rites, I have not permitted them to exaggerate such displays of mourning to include the making of bald spots on their heads and to make incisions in their flesh. As our sages phrased it, “just as the previous verses dealt with the dead, so the verses in front of us deal with honour for the dead.”(Torat Kohanim 1,3)

לא יקרחה קרחה, both he and an ordinary Israelite are not to make bald spots on their heads as a sign of mourning. (compare Deuteronomy 14,1)