If someone has problems with ingrowing hairs when he doesn’t shave (with an electric razor) for a few days–me’ikar hadin can he shave on the week tisha be’av falls on?
For a problem of ingrowing hairs (that cause pain) it is permitted to shave, even in the nine days. If possible, one should avoid shaving at least on the week of Tisha Be’Av.
Sources: Even on Tisha Be’Av itself, we find that it is permitted to treat sores by means of sichah (554:15); likewise, it is permitted to trim the moustach when it causes discomfort in eating (551:13). The same will apply to shaving to prevent ingrowing hairs.