The syndrome of synovitis, acne, pustulosis, hyperostosis, osteitis (SAPHO) encompasses a broad spectrum of cutaneous manifestations associated with osteitic and hyperostotic lesions, which typically may involve the anterior chest wall (ACW). The aetiopathogenetic mechanisms as well as the nosographic framing of the disease are still not fully defined although an important role has been suggested for Propionibacterium acnes (P. acnes). This germ might be able to stimulate both the innate and the T-cell-mediated immune system. The elicited immunological response could be an attempt to eliminate the germ thus inducing the perpetuation of the inflammation. Whether the osteo-articular changes seen in SAPHO could be attributable directly to the infection or to an inflammatory reaction induced by pathogenic material remains a debated issue. The current concept of SAPHO syndrome as a reactive infectious osteitis in genetic predisposed subjects seems appealing, but it has not been yet demonstrated.