Necrotizing cellulitis and fasciitis may be difficult to recognize. When skin necrosis is not obvious, the diagnosis must be suspected if there are signs of severe sepsis (accelerated heart or respiratory rates, oliguria, mental confusion.) and/or some of the following local symptoms or signs: severe spontaneous pain, indurated edema, bullae, cyanosis, skin pallor, absence of lymphangitis, skin hypoesthesia, crepitation, muscle weakness, foul smell of exudates. Many risk factors are suspected. A recent case-control study demonstrated that using ibuprofen increased the risk of cellulitis complicating chickenpox in children. Evidence is lower for other risk factors that are present with a high prevalence in most series: local lesion of skin or mucous membranes (acute or chronic disease, traumatism, surgery.), diabetes, arteriopathy, alcoholism, obesity, immunosuppression, NSAIDs. The risk of streptococcal necrotizing fasciitis is increased when in contact with patients infected by the same streptococcus.