Welcome to HCM
We understand your concerns
As you are well aware the area you mention is most prone to sweat and allergic conditions related to interaction between sweat, dust, detergent or fabric quality of under wear etc. Therefore it is necessary to keep the area hygiene.
Wash the area with warm water and keep it dry for two days. Can use lacto calamine
lotion or mild talcum powder. Consult a physician if itch persists.
Get well soon.