Jeremiah 16:6 - Ellicott's Commentary On The Whole Bible

Nor cut themselves, nor make themselves bald. — Both practices were forbidden by the Law (Leviticus 19:28; Leviticus 21:5; Deuteronomy 14:1), probably in order to draw a line of demarcation between Israel and the nations round, among whom such practices prevailed (1 Kings 18:28). Both, however, seem to have been common, and probably had gained in frequency under Ahaz and Manasseh (Jeremiah 7:29; Jeremiah 41:5; Ezekiel 7:18; Amos 8:10; Micah 1:16). The “baldness” (i.e., shaving the crown of the head) seems to have been the more common of the two.