Why i often have acnes on sensitive part, like my breast?

Acne: Acne occurs due to combination of factors including a generic predisposition. The areas that acne occurs include the face, neck, back and chest commonly. The area where it is involved varies from person to person depending on where the person's largest oil glands are. Friction from clothing rubbing skin especially during exercise can also exacerbate acne. See a dermatologist for treatment options.

Acne: Acne will occur where there are large numbers of sebaceous oil glands like the face, chest and back. It might also worsen from heat and perspiration.