The answer so far
Eyebrow growth, reduced shedding and recovery from a specific hair-loss cause are different outcomes; evidence for one does not establish the others.
A small study found a higher average eyebrow hair count with one GHK-Cu serum than with its comparison serum after 12 weeks. A separate scalp study tested GHK with another ingredient, not GHK-Cu alone. The findings are interesting but do not establish that every serum regrows scalp hair or that injected blends work.12
On this page
Why are copper peptides discussed for hair?
Copper-peptide serums are marketed for skin, eyebrows and scalp hair, but those are different outcomes. A fuller eyebrow, less shedding and recovery from a particular cause of hair loss are not interchangeable. The ingredient is often called GHK-Cu: start with what this copper peptide is, or see what a skin serum is intended to do.1
What did the eyebrow study compare?
In a study published in 2026, 18 healthy adults aged 18–40 with sparse eyebrows received a particular serum described as 2% GHK-Cu on one eyebrow and a matching serum without it on the other. Side assignment was randomised and the study was blinded. After 12 weeks, researchers counted hairs in a photographed square centimetre on each side. This is useful because each participant provided a comparison, but a small trial of one formulation cannot establish that every copper-peptide product works.1
- Eyebrows: 18 adultsA particular GHK-Cu serum was compared with its matching vehicle for 12 weeks.
- One square centimetreAt week 12 the average counts were 30.50 versus 28.67 hairs in the photographed areas.
- Scalp: 45 menA different study tested GHK plus 5-aminolevulinic acid, not GHK-Cu alone.
- Injected blendsNeither study tested GLOW, KLOW or an injected product.
How should I read the numbers?
At the start, the averages were 28.89 hairs in the measured area on the GHK-Cu side and 28.78 on the comparison side. At week 12, they were 30.50 and 28.67 respectively: a side-to-side difference of about 1.83 hairs per square centimetre. That is not a count of new hairs or a baseline-adjusted treatment effect. The report gave p = 0.049 for the week-12 comparison, alongside several other measurements. A statistical result in a small study does not tell us whether a difference will be noticeable to someone else or reliably repeated. Participants also reported higher satisfaction on the GHK-Cu side.1
What did the study say about reactions?
The protocol said people with an adverse patch-test reaction would be excluded; the authors also stated that no allergic reactions were observed during patch testing. They reported no local reactions or adverse events during the 12-week follow-up. That is reassuring for the people and product studied, but 18 participants cannot rule out uncommon reactions or establish long-term safety. Other ingredients and formulations can behave differently. If a cosmetic product irritates your skin, stop using it and ask a pharmacist or clinician for advice. For irritation, allergy and when to seek help, see the skin-reaction guide.15
Did a scalp study test the same product?
A 2016 study followed 45 men with pattern hair loss for six months. It compared two strengths of a topical combination of GHK and 5-aminolevulinic acid with placebo. The authors reported a difference in a hair-count change ratio for one strength versus placebo, but no statistically significant differences in hair length or thickness. The study did not test GHK-Cu alone, and its report does not clearly explain how participants were assigned. It cannot tell us what a particular copper-peptide serum, or an injection, will do to scalp hair. The paper acknowledged public programme support and thanked an individual at a company; that acknowledgment alone does not establish the company’s role.2
Why does the cause of hair loss matter?
Gradual thinning, increased shedding and a new patch of hair loss can have different causes. The American Academy of Dermatology explains that identifying the cause can help guide the next step; a dermatologist or other qualified clinician can assess a change that concerns you. Eyebrow loss can have several causes; for example, alopecia areata can cause patchy loss of eyebrow hair. The eyebrow study enrolled healthy volunteers with sparse eyebrows, so it does not establish a treatment for a diagnosed cause of hair loss. A supplement is not automatically useful just because hair needs nutrients: see what biotin evidence does and does not show. For the broader picture, visit skin and hair health.34
What about GLOW, KLOW or injections?
An eyebrow serum is not the same product or route as an injected peptide or a seller-defined combination. Neither study establishes what GLOW or KLOW does for hair, nor whether a blend is safe or effective. If you are comparing the ideas behind these products, see how GHK-Cu, GLOW and KLOW differ and why the route matters.12
Sources, kept close.
Selected supporting sources; this is not a complete literature review.
- The Efficacy of 2% Copper Peptide (GHK-Cu) Serum for Eyebrow HypotrichosisProcedia of Multidisciplinary Research · Randomized split-face human study
- Efficacy of a Complex of 5-Aminolevulinic Acid and Glycyl-Histidyl-Lysine Peptide on Hair GrowthAnnals of Dermatology / PubMed Central · Small controlled human study, 2016
- Hair loss: Diagnosis and treatmentAmerican Academy of Dermatology · Professional dermatology organisation guidance
- Alopecia areata: Signs and symptomsAmerican Academy of Dermatology · Professional dermatology organisation guidance
- How to test skin care productsAmerican Academy of Dermatology · Professional-society consumer guidance