Pustules are either septic or aseptic; hence, microbiological examination of their content should always be performed. Bacteriological, mycological, and virological examinations are almost always recommended. Although pustules are caused by highly common and prevalent diseases such as acne, rosacea, and folliculitis, it is important to remember that a pustule can also be the primary lesion in certain severe illnesses requiring emergency treatment, such as septicemia and endocarditis. Finally, aseptic pustules can be the dermatological manifestation of many inflammatory diseases such as inflammatory bowel disease or lupus erythematosus.