Hello, I understand your concern for rash on butt line. There can be multiple possibilities of the rash on butt line but most commonly it is seen after a fungal infection. It is due to damp area of the butt line which causes more of fungal infection of the affected area. In my patients I suggest them to apply clotrimazole cream. For itching I prefer to give an antihistamine tablets such as cetrizine or levocetrizine or loratadine for two times a day for few days. Don t try to scratch or rub the area as can lead to further aggravation of the problem of the rash. I also suggest wearing cotton clothes and cotton undergarments to be changed two times a day. Don t wear any synthetic or tight garments. If at all the rash is increasing then can meet a dermatologist for best help. All the best.