TAC1 and acne: Specifically, emotional stresses appear to affect the function of PSUs, contributing to the development and/or aggravation of pre-existing acne via stimulation of (i) hormone production, (ii) neuropeptides, such as corticotropin-releasing hormone (CRH), (iii) melanocortins, such as alpha-melanocyte-stimulating hormone (α-MSH) and adrenocorticotropic hormone (ACTH), and substance P, as well as (iv) proinflammatory cytokines (124).