When oil, dead skin cells, and germs clog the skin's pores, this can cause an outbreak of acne. Swelling, redness, and pus are associated with acne along with pimples. Sometimes, very large and deep pimples are cystic lesions which can become painful or infected and scar the skin. Dr. Schwartz may suggest a strong medicine for cystic lesions or even an alternative treatment. Acne is often hereditary so if one of your parents suffered from acne, you may too.