Severity classification and characteristics of acne The Pillsbury classification is generally used to clinically classify the severity of acne into degrees I-IV. Severity classification of acne Severity. Clinical presentation characteristics. Grade I (mild) Scattered to multiple blackheads, which may be accompanied by scattered inflammatory papules. Grade II (moderate) Degree I + increased number of inflammatory lesions with superficial pustules, but confined to the face. Grade III (severe) Grade II + deep pustules on the face, neck and chest and back. IV degree (severe – clustered) III degree + nodules, cysts with scar formation, occurring on the upper part of the body.