The 43rd prohibition is that we are forbidden from shaving1 the temples of our heads.
The source of this commandment is G‑d's statement (exalted be He),2 "Do not round off the corners of your head."
This prohibition also3 has the goal of preventing us from emulating idol worshippers, since it was the practice of idol worshippers to shave only the sides [of their heads]. For this reason the Sages had to explain in Tractate Yevamos4 that, "Shaving the entire head is also included in the prohibition of 'rounding,'" so that you should not say that the actual prohibition is shaving the temples and leaving the rest of the hair, as the idolatrous priests do; but if you shave the entire head, you are not emulating them. The Sages therefore informed us that it is prohibited to shave the temples in any manner — not by themselves and not with the rest of the head.
One is punished by lashes separately for each side; therefore one who shaves his entire head receives two sets of lashes. We do not count them as two separate commandments although there are two sets of lashes because there are no two phrases [in Scripture] for the one prohibition. If Scripture would say, "Do not round off the right corner of your head nor the left corner of your head," and we would find [that our Sages] stipulated two sets of lashes, then we could count them as two commandments. But since there is only one expression and one type of action, it counts as one commandment. And even though this prohibition is explained as including different parts of the body, and that one receives lashes for each part separately, this does not require it to be counted as more than one commandment.
The details of this mitzvah have been explained at the end of tractate Makkos.5 Women are exempt from this prohibition.6
