- Peninei Halakha
The Rishonim write that one should not get a haircut during the omer period. As we learned above (sections 3-4), Sephardim observe this prohibition until the morning of the 34th day of the omer. Ashkenazic custom, on the other hand, permits it from the morning of Lag Ba-omer, and some are even more lenient, permitting haircuts on the night of Lag Ba-omer. In a time of need, one may rely on those who rule leniently (see above n. 5).
Only regular haircuts, which include an element of joy, are prohibited. However, one may trim his mustache if it interferes with his eating. Similarly, one who gets headaches when his hair is too long, or one who has sores on his head, may cut his hair during this period (based on sa 551:13, mb ad loc. 21, and bhl ad loc.; Siddur Pesaĥ Ke-hilkhato 12:8-9). If one has lice, or one’s child has lice, then if there is no other way to get rid of them, a haircut is permissible.
The prohibition applies to both men and women. However, a woman may cut her hair for purposes of modesty. For example, if her hair comes out of her head covering, she may cut it (sa 551:13, mb ad loc. 79). One may also cut or pluck hair for cosmetic purposes. Therefore, women may pluck their eyebrows or remove facial hair (Piskei Teshuvot 493:7, quoting R. Shlomo Zalman Auerbach; see also Igrot Moshe, yd 2:137).
One may not cut children’s hair during this period, unless there is a great need to do so, such as to prevent them from suffering (see sa 551:14, mb ad loc. 82).
The main participants in a brit mila – the father of the child, the sandak, and the mohel – may cut their hair in honor of the occasion (mb 493:12; we will discuss the status of Yom Ha-atzma’ut below, 4:11). According to Ashkenazic custom, one may cut his hair in anticipation of Rosh Ĥodesh Iyar when it falls out on Shabbat (mb 493:5). Sephardim are lenient in this regard only under pressing circumstances (Kaf Ha-ĥayim 493:42).
Those who follow the customs of Arizal take care not to cut their hair for the entire omer period, until Erev Shavu’ot, when they cut their hair in honor of the festival. According to the custom of Arizal, one should not cut his hair even for the sake of a brit mila. The only exception is cutting the hair of three-year-old boys for the first time on Lag Ba-omer (Kaf Ha-ĥayim 493:13; see below, 5:6 regarding the custom of ĥalaka or upsherin).
 According to Ashkenazic custom, one may shave and cut his hair in honor of Shabbat when Lag Ba-omer falls out on Sunday (Rema 493:2); Sephardic custom prohibits this. If Lag Ba-omer falls out on Friday, however, even Sephardim allow cutting one’s hair and shaving on that day (sa 493:2).