Peptides in scalp care — what they are, how to read the % on a label, and what a cosmetic may claim

"Peptide" appears on almost every scalp serum, but what it means, and what the percentage on the label tells you, is rarely explained.

What peptides are

Peptides are short chains of amino acids — usually 2 to about 50 — far smaller than proteins. In cosmetics they are grouped by how they act on skin: signal peptides that communicate with skin cells, carrier peptides that deliver trace minerals such as copper, and neurotransmitter-inhibiting peptides used in anti-wrinkle products [1][2].

Familiar scalp examples include Copper Tripeptide-1 (GHK-Cu), a long-studied carrier peptide [3], and Acetyl Tetrapeptide-3 and Biotinoyl Tripeptide-1, signal peptides modified to penetrate skin better [2]. The INCI suffix tells you the chain length: tripeptide = 3 amino acids, tetrapeptide = 4.

How to read the %

A figure like "3%" in marketing usually means the percentage of the supplier's complex, not of pure peptide. Those complexes are mostly water, glycerin or botanical extract, with the peptide itself at parts-per-million levels — which is normal, because signal peptides act at very low concentrations [1][2]. What the % really tells you is whether the maker used the complex at the supplier's recommended level — a question worth asking.

Two more worth asking: does the formula help the peptide cross the skin barrier, since peptides are hydrophilic and penetrate poorly on their own [1][2]; and is it free of likely irritants for delicate skin, such as high alcohol or fragrance, which matters for a daily leave-on product.

Where the evidence stands

Honestly: most evidence for cosmetic peptides comes from laboratory work, small studies and ingredient suppliers. Peer-reviewed reviews agree that large controlled human trials are scarce [1][2]. That does not mean peptides do nothing; it means what to expect from a cosmetic is conditioning of the scalp and the look of the hair, not a medical effect.

What a cosmetic may and may not say

Under Thailand's Cosmetics Act B.E. 2558, a cosmetic is an external product for cleansing, conditioning or changing appearance; it must be notified to the Thai FDA before sale, and advertising must not be false, exaggerated or imply drug-like properties [4]. Claims such as "treats hair loss", "regrows hair" or "new hair growth" are therefore outside what a cosmetic should say. Within scope: conditioning the scalp and roots, less breakage when combing, and hair that looks fuller.

The EU applies the same logic through six common criteria for cosmetic claims — legal compliance, truthfulness, evidential support, honesty, fairness and informed decision-making — and states that extending an ingredient's properties to the finished product requires evidence it is present at an effective concentration [5].

In short

• Peptides are short amino-acid chains that act at low concentrations
• The % is usually the complex, not pure peptide — ask whether it is used at the recommended level
• Expect cosmetic, not medical, effects
• Promises beyond cosmetic law are a warning sign

ONE PEN uses ten complexes including Copper Tripeptide-1, Acetyl Tetrapeptide-3 and Biotinoyl Tripeptide-1 in an alcohol-free formula — conditions the scalp and hair roots · less breakage when combing · hair looks fuller and weightier · cosmetic notified with the Thai FDA.