Rabbi Mendel Bluming is often asked by members of his congregation in Potomac, Maryland, about the 9 days practices, days on which we mourn the destruction of the Holy Temple.
Traditionally freshly laundered clothing is not worn for the duration of
this period (other than Shabbat), however that is only if they are changed because
of comfort or pleasure. Those who are accustomed to changing their shirts
regularly due to dirt or perspiration in the heat of summer, may do so even
during the nine days, even if the shirt has previously been freshly laundered.
Menachem Mendel Bluming quoted from Rabbi Goldstein at
ShulchanAruchHarav.com who sources this in Kinyan Torah 1:109; Piskeiy Teshuvos
551:17