Acne happens when the body over produces sebum (a natural oil that your skin secretes to protect itself from drying out). This can happen for a number of reasons such as medications and hormone imbalances.
Acne occurs when the pores and minute hair follicles in our skin become blocked and inflamed by the sebum, dead skin cells and bacteria. The result being acne (blackheads, whiteheads, pimples and cysts). Once this begins to settle it can cause hyper-pigmentation of the skin along with marks and scars. Serve acne such as cystic acne can damage the dermis and lower layers of the skin, causing the tissue to scar.