Acne is from skin irritation, blocked pores, bacteria and oil secretion in the skin. If your outbreak is sudden, go back and look at any predisposing factors such as oil containing skin products, a new exercise regimen with excessive sweating, or even a new hair style with hair rubbing on your skin. The answer may be simple elimination of an irritation.
Sometimes acne will present with no apparent reason. The treatment is then daily maintenance. Face washing 2-3 times a day is a must. Use of over-the-counter topical acid products and benzoyl peroxides are very helpful. It takes six weeks for acne treatments to start working. As acne is improving, it will leave a temporary "dark area" in the skin. This "dark area" is not scar and will disappear with time - usually many months. If you continue to get new acne despite daily maintenance, you should consult your dermatologist.