Hello,
It can be due to sweat dermatitis, moisture(due to sweating or frequent washing), the abrasion caused by clothing, the pressure of sitting, chemical irritants like laundry soaps, colognes and scented toilet paper, certain food irritants, infections like STD’s
and pinworms, anal abrasions
and fissures
and skin problems such as psoriasis, seborrhea and eczema.
Apply cool compresses on the area and take bath with cool(not very cold) water.