They result when sebaceous material from the comedo gets into the surrounding tissue and causes an inflammatory reaction. Picking and squeezing acne lesions is a frequent cause of lesion rupture and inflammation, which increases the risk for scarring. For this reason, it is important to leave acne lesions alone. Papules and pustules are relatively small, while nodules are larger, more severe acne lesions. Papules are mildly inflamed, showing redness but no apparent pus.
Pustules are small, like papules, but are clearly inflammatory.
Pustules are small round lesions that contain visible pus. The pus is underneath the surface of the skin. Pustules do not usually contain a lot of bacteria. The inflammation is generally caused by chemical irritation from sebum components such as free fatty acids. They are large inflammatory lesions that contain large amounts of pus.