Peppermint oil is an inexpensive, menthol-rich plant oil used diluted on the scalp for hair regrowth. Its appeal rests on a single animal study and a plausible blood-flow mechanism, but human evidence is essentially absent. The main downside is scalp irritation, manageable with dilution and a patch test; the promise remains unproven. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Ferritin | 50–100 ng/mL | Low iron stores are a common, reversible cause of hair shedding |
| Transferrin saturation | 25–35% | Confirms true iron status when ferritin is ambiguous |
| Vitamin D (25-OH) | 40–60 ng/mL | Low vitamin D is associated with hair shedding and follicle cycling problems |
| Zinc | 90–120 µg/dL | Zinc deficiency can cause hair loss; reversible with correction |
| TSH | 1.0–2.0 mIU/L | Thyroid dysfunction is a common reversible cause of diffuse hair loss |
| CRP (high-sensitivity) | < 1.0 mg/L | Helps interpret ferritin and flags scalp/systemic inflammation |
Cadence: Baseline before starting; re-check any abnormal value after ~3 months of correction, otherwise every 6–12 months only if hair loss persists.