Adam Clarke on Leviticus 21:5

They shall not make baldness - See the note on Lev 19:27. It is supposed that these things were particularly prohibited, because used superstitiously by the Egyptian priests, who, according to Herodotus, shaved the whole body every third day, that there might be no uncleanness about them when they ministered in their temples. This appears to have been a general custom among the heathen. In the book of Baruch 6:31, the priests of Babylon are represented sitting in their temples, with their clothes rent, and their heads and beards shaven, and having nothing upon their heads. Every person knows the tonsure of the Catholic priests. Should not this be avoided as an approach to a heathenish custom?