A laboratory-made copy of a small human protein added to scalp serums. Rodent fur regrowth is consistent, but no controlled study in people has measured hair count or thickness, the one test on living human scalp follicles pointed the other way, and the protein is far larger than what passes through intact skin. Years of scalp use are untested. (Full Review)

Protocol

Standard cosmetic approach

0.5–1 mL, once or twice daily

Roughly 1–100 ppm in a scalp serum, applied to a dry scalp

Best time of day

Evening, dry scalp

Left overnight for contact time; no circadian data exist

Single versus split dosing

Twice daily over one dose

Short residence time argues for split dosing; no dose-response study exists

Time to effect

Accelerated closure of chronic skin wounds

Within 3 months

About 25% of venous ulcer patients reached complete closure at the 0.03% dose

Visible change in hair

3–4 months

The hair cycle sets the floor; earlier judgements measure shedding variability

Fair assessment

12 months

No measurable change by 12 months has no plausible explanation other than non-response

Benefits

Medium: Accelerated closure of chronic skin wounds

Speculative: Faster regrowth after hair loss — conflicted; greater hair shaft density and follicle number; increased blood supply around the follicle; reduced scalp inflammation

Contraindications

Active malignancy, or epithelial cancer in remission under five years

Pregnancy and lactation

Active scalp infection, open wounds or untreated scarring alopecia

Competitive athletes under World Anti-Doping Agency (WADA) jurisdiction

Hypersensitivity to the peptide or residual E. coli host-cell protein

Solid-organ transplant recipients on maintenance immunosuppression

Key Interactions

Topical minoxidil (caution, additive)

Microneedling and fractional lasers (caution, potentiating)

Topical retinoids (tretinoin, adapalene) (caution)

Anticoagulants and antiplatelet agents (aspirin, clopidogrel, apixaban) (caution)

Platelet-rich plasma and exosome scalp injections (caution, additive)

Over-the-counter medicated shampoos (ketoconazole 2%, salicylic acid, coal tar) (monitor)

Supplements with additive angiogenic or vasodilatory effects (L-arginine, L-citrulline, beetroot, Ginkgo biloba) (monitor)

Supplements that plausibly oppose the mechanism (high-dose curcumin, epigallocatechin gallate, resveratrol) (monitor)

Oral finasteride or dutasteride (no interaction, complementary)

Risk & Side Effects

High: Mild, self-limiting adverse events during short-term dosing

Low: Reduced hair shaft production in human scalp follicles — conflicted; transient rise in a tumour marker; application-site reactions; transient anti-drug antibodies

Speculative: Tumour promotion through angiogenesis and cell migration; impurities and mislabelling in research-only vials; unwanted hair growth beyond the application area

Monitoring

Marker	Target	Why
Serum ferritin	70–100 (women), 100–150 (men) ng/mL	Low iron holds follicles in the resting phase
25-hydroxyvitamin D	40–60 ng/mL	Receptor signalling is required for follicle cycling
TSH	0.5–2.0 mIU/L	Common reversible cause of diffuse shedding
Serum zinc	90–120 µg/dL	Deficiency causes shedding and brittle shafts
Total and free testosterone, DHEA-S	Mid-to-upper sex- and age-specific reference, not above	Androgen excess drives follicle shrinkage
Haemoglobin (complete blood count)	13.5–15.0 (women), 14.5–16.5 (men) g/dL	Anaemia drives diffuse shedding
Squamous cell carcinoma antigen	≤1.5 ng/mL	Baseline for the theoretical tumour-promotion signal
Hair count and terminal-to-vellus ratio (phototrichogram)	No established target; change from baseline over a tattooed 1 cm² zone	The only direct read-out of regrowth

Cadence: Baseline panel before starting; tumour marker and skin check at 6 and 12 months; photography and hair census at 4, 8 and 12 months, then annually

Qualitative Assessment

Volume of hair shed during washing and brushing, over a fixed weekly routine
Scalp visibility under overhead lighting, the earliest noticeable change
Perceived shaft thickness and styling product needed to hold a shape
Scalp comfort — itching, burning or tightness after application
Rate of hairline regrowth between haircuts, at a fixed interval

sh-Oligopeptide-4 for Hair Regrowth

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment