IGF1 and acne: Bifidobacteria may also influence acne development by modulating insulin-like growth factor 1 (IGF-1), a key hormone linked to acne severity.1 Elevated IGF-1 promotes hyperkeratinization, proinflammatory cytokine secretion, sebocyte proliferation and lipogenesis,48 all of which contribute to the formation of comedones and a growth medium for acne-causing bacteria.