Guide
What Are Peptides?
A plain-English introduction to peptides, the difference between cosmetic ingredients and medicines, and how to judge product claims.
Published 20 October 2026 · Last reviewed 20 October 2026 · Editorial content by the Peptide Atelier UK team, not clinically reviewed
Editorial standards and corrections
A plain-English definition
Peptides are short chains of amino acids, the same building blocks that make up proteins. Where a protein may contain hundreds of amino acids folded into a complex shape, a peptide typically contains between two and around fifty.
The word covers an enormous range of substances. Some peptides occur naturally in the body, some are made in laboratories for cosmetic formulations, and some are active ingredients in prescription medicines. Knowing that something is a peptide tells you very little about what it does or whether it is safe.
Cosmetic peptides versus medicinal peptides
In the UK, a cosmetic product is intended to be applied to the external parts of the body to clean, perfume, change the appearance of, protect or keep it in good condition. Cosmetic peptides are used for those purposes and are regulated under cosmetics law.
A medicine is a substance presented as treating or preventing disease, or used to restore, correct or modify physiological functions. Peptide medicines such as semaglutide are regulated by the MHRA, must be authorised before they can be marketed, and are usually prescription-only.
Examples of peptide ingredients in skincare
These names appear in the INCI ingredient list on cosmetic packaging. Concentrations are rarely disclosed, and the effects reported in laboratory studies do not automatically translate into a finished product.
- Copper Tripeptide-1 (often referred to as GHK-Cu)
- Palmitoyl Tripeptide-1 and Palmitoyl Tetrapeptide-7
- Acetyl Hexapeptide-8
- Palmitoyl Pentapeptide-4
Licensed medicines and experimental compounds
A licensed (authorised) medicine has been assessed for quality, safety and efficacy for specific uses. An experimental or investigational compound has not completed that process. Some compounds are sold online with labels such as 'research use only'. That label does not make them safe or lawful to use on people, and it does not make them lawful to sell for human consumption.
Why route of administration and formulation matter
A peptide applied to the skin in a cosmetic serum behaves very differently from the same molecule injected into the body. Skin is an effective barrier, and topical products are designed to act on the surface layers. Injectable products bypass that barrier and carry very different risks, including infection, contamination and dosing errors.
How to evaluate claims and documentation
- Look for a full INCI ingredient list and the responsible person's details on cosmetic packaging.
- Be cautious of words such as 'clinically proven', 'medical grade' or 'guaranteed results' without references.
- Check whether a claimed study looked at the finished product, an isolated ingredient, cells in a dish or animals.
- For medicines, only use products prescribed by a registered healthcare professional and dispensed by a registered pharmacy.
Frequently asked questions
Are peptides safe?
It depends on the specific peptide, the finished product and how it is used. Cosmetic products require a product-specific safety assessment; the word 'peptide' alone does not establish safety. Unregulated injectable products cannot be assumed safe.
Do cosmetic peptides work like medicines?
No. Cosmetics are not permitted to claim medical effects, and topical cosmetic peptides should not be expected to produce medicinal results.