sh-Polypeptide-9, a cosmetic ingredient copying the body's own blood-vessel growth signal, is sold in hair serums and scalp injection kits for thinning hair. Studies of mixtures containing it, mostly needle-delivered, report more and thicker hair; its own contribution remains unknown. The documented risks come mainly from the injection process. For people committed to treating thinning hair, it is a plausible, generally well-tolerated add-on resting on low-quality, commercially shaped evidence. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Ferritin | 70–150 ng/mL | Iron stores for hair growth |
| TSH (thyroid-stimulating hormone) | 0.5–2.5 mIU/L | Thyroid-related shedding |
| 25-hydroxyvitamin D | 40–60 ng/mL | Deficiency linked to hair loss |
| Zinc (serum) | 90–120 µg/dL | Deficiency causes shedding |
| Total testosterone and DHEA-S (dehydroepiandrosterone sulfate) in women | Testosterone 15–45 ng/dL; DHEA-S within the lower half of the age-specific range | Screens for excess male hormones |
| CBC (complete blood count) with platelets | Platelets 150–400 × 10³/µL | Bleeding risk and anemia before injections |
| Hair density (trichoscopy, magnified scalp imaging) | No established target; track change from own baseline (hairs/cm²) | Primary measure of regrowth |
| Hair shaft diameter | No established target; track change from own baseline (µm) | Measures thickening |
| Hair-pull test | 2 or fewer hairs per pull of about 60 hairs | Tracks active shedding |
Cadence: Baseline blood tests, photographs and trichoscopy before the first session, with a dermatologist skin check within the prior 3 months typically included; repeat photographs and trichoscopy at 3, 6 and 12 months, then every 6–12 months during maintenance; abnormal baseline blood values typically rechecked 3 months after correction.