Q. Can you take a haircut or go to the hairdresser on Purim?

A. Divrei Malkiel (5: 237) and Pischei Sheorim (Megilla 5b) mention that although working in Purim is permitted when it is needed for the day (O.H. 696: 1), one should avoid taking a haircut and cutting nails, so he will prepare and groom himself properly before Purim. Nitey Gavriel (Purim 66 : 7) quotes diverse opinions, and some permit only a haircut done by a Gentile even if Purim falls on an Erev Shabbos.
Horav Shlomo Miller’s Shlit”a opinion is to be lenient when in need.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a