# Peptides

> Source: https://thecastindex.com/beauty/ingredients/peptides — updated 2026-09-25

Peptides are short chains of amino acids. In cosmetics they are used to condition skin, lips, lashes and hair, and some are marketed as “signal” peptides for the look of firmness. Evidence varies widely between specific peptides, so treat broad claims cautiously and judge each formula on its full ingredient list.

- Also on labels as: Palmitoyl tripeptide, Palmitoyl pentapeptide-4, Acetyl hexapeptide-8, Copper peptides
- Type: Signal and conditioning molecules

## What it does

- Conditions and softens lips, skin and hair in many formulas
- Some peptides are studied for the appearance of fine lines, with mixed evidence
- Hair “bond” and repair treatments use peptide technology to condition damaged hair

## Who it suits

Most people; peptides are generally gentle and suit sensitive skin.

## How to use it

1. Use as directed — peptides appear in serums, lip treatments, masks and hair treatments
2. Layer skincare peptides before moisturiser

## Take care

- Evidence differs by peptide; brand claims are often based on the brand’s own studies
- Some brands advise against mixing copper peptides with strong acids or vitamin C

## What it pairs with

Generally compatible with hydrators and moisturisers. Follow product directions on combining with acids or vitamin C.

## Products in the catalogue that list it

- [Rhode Peptide Lip Treatment](https://thecastindex.com/beauty/rhode-peptide-lip-treatment)
- [Rhode Peptide Lip Tint](https://thecastindex.com/beauty/rhode-peptide-lip-tint)
- [Medicube PDRN Pink Peptide Serum](https://thecastindex.com/beauty/medicube-pdrn-pink-peptide-serum)
- [Fenty Beauty Gloss Bomb Universal Lip Luminizer](https://thecastindex.com/beauty/fenty-beauty-gloss-bomb-universal-lip-luminizer)
- [K18 Leave-In Molecular Repair Hair Mask](https://thecastindex.com/beauty/k18-leave-in-molecular-repair-hair-mask)
- [Olaplex Bond Shaper Curl Rebuilding Treatment](https://thecastindex.com/beauty/olaplex-bond-shaper-curl-rebuilding-treatment)

## Questions

### Do peptides really work?

It depends on the peptide. Some have published studies, often small or brand-funded; others have little evidence. They are generally gentle conditioning ingredients.

### Why are peptides in lip products?

They are used as conditioning ingredients alongside emollients such as shea butter to keep lips feeling soft and smooth.

## Sources

- [Ferreira et al., “Cosmeceutical Peptides in the Framework of Sustainable Wellness Economy”, Frontiers in Chemistry, 2020](https://pubmed.ncbi.nlm.nih.gov/33195061/)

General information, not medical advice.