What Does a Peptide Hair Serum Do?

October 27, 2026

A peptide hair serum is a leave-in treatment for hair that's been lightened, coloured or heat-styled. Peptides are short chains of amino acids, the same building blocks as the keratin your hair is made of, and a peptide serum puts them onto your hair to help it feel stronger and look shinier.

If you've been looking for an alternative to K18 or Olaplex, the Amethyste Biomimetic Molecular Repair Leave-In Serum by FarmaVita is a peptide leave-in that takes just 4 minutes after you wash. Here's what's in it, how it works and how to use it.

What is the Amethyste Biomimetic Molecular Repair Leave-In Serum?

It's a leave-in treatment for hair that has been through bleach, colour, other chemical services or a lot of heat styling. You use it after shampooing, on towel-dried hair, leave it for 4 minutes and don't rinse it out, so it fits straight into wash day before you style.

It comes in five 5 ml vials, and you use 2 to 5 ml at a time, depending on your hair's length and thickness. The formula is vegan.

Where does hair get its strength?

Hair gets its strength from bonds inside the fibre. Hydrogen bonds break and re-form every time hair gets wet and dries again, which is why a blow-dry drops out in the rain. The stronger disulphide bonds hold together the protein in the cortex, the inner part of the hair.

Lightening and permanent colour work on those disulphide bonds, and each service adds to the change. That's why lightened hair can feel more porous than it used to, and why peptide treatments aim to work inside the hair fibre, not just coat the surface.

What's in the serum?

The serum is built around the Biomimetic Tri-Peptide Complex. "Biomimetic" means it's designed to copy a natural structure.

The peptide is made in a lab rather than taken from animal or plant protein. It conditions your hair and leaves a light film on the surface.

Alongside it, ProGloss Tech is added for shine and softness.

What results can you expect?

Used as directed, the serum helps reverse up to 3 years of damage from bleach, colour, chemical services and heat, and restores up to 91% of hair's original strength.*

*Based on instrumental testing by an external laboratory: fatigue cycles, DSC scanning and luminosity analysis. Results may vary depending on hair type and condition.

How do peptides work on hair?

Size matters. Small peptides can travel into the hair fibre, while very large proteins mostly stay on the surface as a film. That's why treatments for lightened and coloured hair are being built around peptides.

Because this serum is a leave-in, it stays on your hair after washing rather than being rinsed away.

Which shampoo should you use with it?

The directions are to wash with an Amethyste shampoo first and to skip conditioner and masks on the days you use the serum. That keeps the step before the serum simple: a clean, towel-dried base for the leave-in to go onto.

Pick the shampoo for your hair. The Amethyste Chroma Color Protective Shampoo is made for colour-treated hair, and the Amethyste Nutri Nutritive Repair Shampoo is the nourishing option for dry hair. On washes between serum days, you can go back to your usual conditioner or mask.

How do you use the serum?

Wash with an Amethyste shampoo. Skip conditioner and masks on the days you use the serum.
Towel-dry well. Hair should be damp, not dripping: about 65% wet.
Apply 2 to 5 ml. Use less for short or fine hair and more for long or thick hair.
Leave for 4 minutes. Don't rinse it out.
Style as usual.
Use it for 5 washes in a row, then every 3 to 4 washes to keep hair feeling strong.

Pro Tip: Start the first 5 washes straight after a colour or lightening appointment, and set a reminder for every third or fourth wash after that so the routine sticks.