My 18 year old son has raised red itchy skin. mainly in groin area, on buttocks and under arms. ?

Rash: This would require examination to be able to properly assess.

Rash: May be fugal- which often is itchy and thrives in warm moist areas or bacterial. Does he shave there?Can promote bacterial infection from nicks. Wash w/ soap, do not shave, keep dry w/ loose cotton clothing that allows for ventilation. Rinsing area with vinegar in shower may help w/ fungus , anti fungal cremes may help but F/U/W MD as may need oral & topical antibiotics for bacterial rash