Any form of scarring of the skin occurs mainly because of injury to it s deeper layer the dermis. This injury is more pronounced if the acne is more inflamed or infected. Inflammation occurs because the follicle usually gets blocked with oily secretions, bacteria and dead cells & if the follicular wall ruptures, it ends up damaging the surrounding healthy skin. Wound healing occurs with fibrosis, and it is this fibrosis which causes the scarring. This scarring is more pronounced with pustular or cystic acne and less so with the blackheads and whiteheads (which are more superficial lesions). Ways to prevent scarring are to avoid the inflamed lesions for which you should visit a dermatologist who would give you topical or oral treatment. For your whiteheads, a topical retinoid would most probably be prescribed. Also the good habit of not picking your acne must persist. Even with the utmost care, you may sometimes end up with some scarring. For this various procedures are available to decrease their appearance. These are based on the principle of collagen boosting as well as breaking of the fibrosed bands. Some of these include chemical peeling, fractionated CO2 or Er:YAG lasers, dermarollers, demabrasions etc with or without subcision of the scars. Visit a nearby dermatologist for more details on each procedure.