Acne inversa or hidradenitis suppurativa (HS) is a disease that usually begins as pimple-like bumps on the skin. The pimple-like bumps tend to develop in places where everyday pimples do not appear. HS is most common on the underarms and groin. Getting treatment for HS is important. Early diagnosis and treatment can prevent HS from worsening. If HS worsens, the pimple-like bumps can grow deep into the skin and become painful. They can rupture, leaking bloodstained pus onto clothing. This fluid often has a foul odor. As the deep bumps heal, scars can form. Some people develop tunnel-like tracts under their skin. As the skin continues to improve and scar, the scars thicken. When thick scars form in the underarm, moving the arm can be difficult. Thick scars in the groin area can make walking difficult. Because HS can look a lot like acne, folliculitis, or boils, it is best to see a dermatologist for a diagnosis.