This review provides a new insight into the participation of neuropeptides, notably substance P (SP), in the pathophysiology of acne. We show morphological alterations of sebaceous glands elicited by SP and differences in expression of various neurogenic factors in association with sebaceous glands in acne-prone versus normal facial skin. In vitro studies reveal that SP promotes both the proliferation and the differentiation of sebaceous glands. SP induces the expression of neutral endopeptidase, a potent neuropeptide-degrading enzyme, in sebaceous germinative cells and of E-selectin by perisebaceous venules. Facial skin from acne patients is characterized by rich innervation, by increased numbers of SP-containing nerves and mast cells, and by strong expression of neutral endopeptidase in sebaceous glands and E-selectin in venules around sebaceous glands, compared with normal skin. Mast cell-derived IL-6 and TNF-alpha, followed by SP-stimulated degranulation, have the potential to induce nerve growth factor expression by sebaceous cells which results in the promotion of innervation and in the expression of E-selectin, respectively. SP enhances mast cell proliferation through up-regulation of stem cell factor expression in fibroblasts. These findings suggest the involvement of neurogenic factors, such as neuropeptides, in the disease process of acne and explain the possible mechanism of the exacerbation of acne from a neurological point of view.