TGF-beta1 (scalp growth inhibitor)
The molecule that tells your hair follicles to quit. DHT hires it. It's why you're balding.
Grounded in the research on Transforming growth factor beta 1
What it actually is
TGF-beta1 (Transforming Growth Factor beta 1) is a signaling protein your cells use to say 'stop dividing.' It's everywhere in your body, but on your scalp it's the kill switch for hair growth. When TGF-beta1 gets switched on in a follicle, that follicle exits its growth phase early and goes dormant. Encoded by the TGFB1 gene, it's part of the TGF-beta superfamily that controls cell growth, differentiation, and apoptosis (programmed cell death).
The DHT handoff (the mechanism)
Here's the chain in male-pattern baldness. Testosterone gets converted to DHT (dihydrotestosterone) by the enzyme 5-alpha-reductase. DHT binds androgen receptors in the dermal papilla cells at the base of each follicle. Inoue, Hibino and others (2006, J Clin Invest) showed those activated papilla cells then secrete TGF-beta1, which signals the keratinocytes above to stop proliferating. DHT doesn't kill your hair directly. It hires TGF-beta1 to do it.