Acne is typically found on the face, neck, upper arms and back. A few isolated black heads may occur on the legs. In general, acne in the groin area is rare and is infact never acne. Acne has typical lesions but can often be confused with other skin lesions. When you have pustules or pimples in the genital area, the diagnosis of acne should always be questioned.
Skin lesions or pustules in the genital area are most likely related to an infection of the hair follicles (folliculitis). This disorder can occur from ingrown hairs or may even occur after shaving. The shaving can cause pulling of the hair and can result in pimples along the hair line. The treatment for folliculits is simply observation. There is not need for any antibiotics. The condition usually resolves on its own.
Another condition which may appear like acne in the genitals is a condition called Hidradenitis Suppurativa. Hidradenitis Suppurativa is also known as 'Acne Inversa'. It is a physically, emotionally, and socially disabling disease affecting creased areas of the body (Arm pits, groin, breast line). It usually occurs where both sweat glands and hair follicles are found. It is not infectious and recurrent; typically manifesting as a progression from single boil-like, pus-filled abscesses, or hard lumps, to painful, deep-located, often inflamed clusters of painful lesions with continuous drainage of fluid.
Any rash in the genital areas has multiple other causes and acne is very unlikely.
If the condition is not painful and not associated with any other features and is mild in nature and not prolonged, observation is recommended. If the condition is bothersome, the best advice is to see a dermatologist and have him/her examine you.