A laboratory-made copy of a natural human signalling protein, sold in scalp serums. The biology behind it concerns hair colour more than hair thickness, and no study has tested the ingredient on its own. The protein is large enough that intact skin should block it, and nearly all supporting material comes from the companies selling it. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Total hair density (1 cm² target area) | No established target; usual trial threshold is a gain of 10 or more hairs/cm² from baseline | The only direct measure of whether anything is working |
| Terminal-to-vellus hair ratio (1 cm² target area) | At or above 4:1 | Distinguishes recoverable thinning from follicles already lost |
| Ferritin | 70-100 ng/mL (women); 100-150 ng/mL (men) | Iron stores set growth-phase length |
| 25-hydroxyvitamin D | 40-60 ng/mL | Vitamin D receptor activity is required for follicle cycling |
| TSH | 0.5-2.0 mIU/L | Thyroid dysfunction causes diffuse shedding that mimics treatment failure |
| Serum zinc | 90-120 µg/dL | Zinc deficiency shortens the growth phase and thins the shaft |
| Serum total tryptase | Below 8 ng/mL | Flags the expanded mast-cell population most likely to react to a mast-cell growth signal |
Cadence: Baseline, then 3, 6 and 12 months; scalp photographs every 4 weeks during the first 3 months; deficiency panel repeated at 6 months if abnormal at baseline and annually thereafter.