Between the 17th of Tammuz and Tisha B'av
14. When the thirty days of mourning [during which a mourner may not cut
his hair or shave] are concluded on the eighteenth of Tammuz or afterward
until Rosh Chodesh Av, the mourner may cut his hair (and shave) (1). From
Rosh Chodesh Av onward, a person is forbidden to wash his clothes or cut
his hair (or shave), even under such circumstances (2).
(1) Although our custom is to refrain from haircuts from the 17th of Tammuz
onwards, since this person has been mourning for thirty days already, he is
granted this leniency.
(2) In a case of necessity, if the thirty day mourning period ended between
Rosh Chodesh Av and the week in which Tish'ah B'av occurs, the mourner may
take a haircut or shave, but not during the week that Tish'ah B'av occurs
(see Mishna Berura 551:87 and Sha'ar Hatziyun 93).