Also known as a boil, this type of infection is quite painful. It forms itself around hair follicles. It all starts as a small, tender red bump, but then it gets larger and filled with pus. If shouldn’t be left untreated because it can develop into an abscess. Contrary to folliculitis, which only affects the hair follicle, this infection takes over the whole pilosebaceous unit. These units are located throughout the body and make up the shaft, follicle, sebaceous gland, and arrector pili muscle. Consequently, the symptoms appear on the face, neck, armpits, buttocks, and thighs.