The 166th prohibition is that a regular kohen is forbidden from becoming tameh (unclean)for any dead person other than the relatives listed in the Torah.1
The source of this prohibition is G‑d's statement2 (exalted be He), "He shall not become tameh through the dead of his people."
One who transgresses this prohibition and becomes tameh for anyone other than the six3 specified relatives is punished by lashes.
This prohibition does not apply to women. The Oral Tradition4 explains the phrase,5 "Sons of Aaron," to mean, "Only the 'sons of Aaron,' not the daughters of Aaron."