Question:
Am I allowed to trim my shaitel during the three weeks?
Answer:
Although we do not take haircuts during the three weeks, nevertheless, it is permitted to trim or cut a shaitel or wig during the three weeks. Although it looks like a person's hair, it isn't part of the person's body, and no different than any other article of clothing that may be trimmed or washed during the three weeks. During the nine days one should not wash or cut a wig.
Sources:
Be'er Moshe 7-5, Kol Hamisablim Aleha chap. 3-4(4), Shevet Hakehosi 4-150 (3), Kovetz Halachos (Bein Hamitzarim) 13-12, Nitei Gavriel (Bein Hamitzarim) 21-5,
