Hi,u r right ,that this lesion r related to sweat, irritation, & overweight
. u have frictional dermatitis
.Overweight patient have more skin to skin contact & in between the skin fold
sweat retend that cause irritation & this lead to dermatitis.When dermatitis heals it lead postinflammatory pigmentation. My advice is that reduce ur weight & wear cotton short so that skin to skin contact not occur.