Peptides in Skincare: Why They Work in Parts per Million

Peptides are messages, not building blocks, and they work at hundreds of ppm. A peptide near the top of an ingredient list is a warning, not a boast.

Ingredients
13 AUG 2026
7 min read

Peptides in skincare are short chains of amino acids that act as messages rather than as building material, and they are used at hundreds of parts per million rather than at percentages. A peptide near the top of an ingredient list is a warning, not a boast, because at that position you are almost certainly reading about the water it arrived in.

That single fact reorganises the whole category. Once you know the scale a peptide works on, most peptide marketing becomes easy to sort.

What a peptide is, and what it is not

Amino acids link into chains. A short chain is a peptide. A long chain is a protein. Collagen is a protein, and that is where the confusion in this category begins.

Applying collagen to skin does not add collagen to skin. The molecule is far too large to cross the outer layer, and the interesting peptides were never building blocks anyway.

They are signals. A peptide sequence can resemble a fragment the body produces during normal turnover, and the presence of that fragment can read to surrounding cells as information. The sequence is the active part. Change it and you have a different ingredient with different behaviour, which is why "contains peptides" on a front panel means almost nothing.

The four groups

Signal peptides. Fragments resembling the pieces released when the skin's own matrix breaks down. The proposal is that their presence reads as a prompt to build.
Carrier peptides. Peptides that transport a trace mineral, usually copper. The mineral is the point and the peptide is the vehicle.
Enzyme-inhibiting peptides. Intended to slow the enzymes that break down structural proteins.
Neurotransmitter-inhibiting peptides. The group acetyl hexapeptide-8 belongs to. In cell studies it interferes with the protein complex that releases signalling chemicals at a nerve ending.

These are categories of intent. They describe what a formulator was reaching for, not what happens on your face, and the evidence behind each group varies widely.

Why peptides in skincare work in parts per million

Signalling molecules act at low concentrations by design. Biology does not use a message at 20 percent, because a signal that requires that much material is not really a signal.

Acetyl hexapeptide-8 is a good worked example. Our 03 wrinkle ampoule uses it at 500 ppm, which is 0.05 percent. Compare that with the niacinamide in our own 01 pore ampoule at 210,000 ppm, and you are looking at two ingredients that live four hundred times apart on the same scale.

Neither number is a score. They are two different jobs with two different sensible ranges, which is the single most misread idea in ingredient marketing.

The percentage trap

Here is where the category gets genuinely misleading, and it is worth understanding before your next purchase.

Peptide raw materials are almost never supplied as dry powder to a formulator. They arrive pre-diluted, as a trade solution in water or glycerin, at a small fraction of active peptide. When a carton advertises a large percentage of a named peptide, that figure very often refers to the supplied solution and not to the peptide itself.

So a serum boasting ten percent of a peptide may contain a great deal of water, a modest amount of glycerin, and an amount of actual peptide that would look unimpressive if printed honestly. Nothing illegal has happened. You were simply told about the bucket rather than what was in it.

What the label says	What it may actually mean	How to check
10 percent peptide	10 percent of a pre-diluted trade solution	Look for the word solution or complex next to the figure
Peptide listed third on the INCI	Mostly the water and glycerin the peptide shipped in	Check whether the diluent appears separately at all
500 ppm of a named peptide	0.05 percent of that specific molecule	The unit is small, so the figure is probably the peptide
Peptide complex, no figure	Unknown, and unknowable from the carton	Position on the ingredient list is your only clue

An ingredient list is ordered by weight, and that ordering is a legal requirement rather than a courtesy. It is the one part of a label nobody can dress up. If you learn to read position instead of headline numbers, you need very little else. The arithmetic behind all of these units is in ppm, percent and parts per billion.

Trace levels, and what they are for

Some peptides appear in a formula at levels far below the ones above. Not hundreds of parts per million, but parts per billion.

At that scale an ingredient is on the list rather than in the product in any meaningful sense. It is there so a name can appear on a carton. Our own 03 formula carries two additional peptides at trace levels of exactly this kind, well below the acetyl hexapeptide-8 the ampoule is named for, and we do not build a single claim on either of them.

We are pointing at our own label because the practice is everywhere and it is easier to see when someone shows you their own. When you find a famous peptide sitting near the very end of an ingredient list, immediately after the preservatives, you have found label dressing.

The injectable comparison, and why it fails

Acetyl hexapeptide-8 is regularly marketed with language borrowed from injectables. The comparison is a marketing move rather than a technical claim, and it breaks on three points.

Route. An injectable is delivered into muscle by a clinician with a needle. A cosmetic is applied to the surface of an intact barrier.
Molecule. The two are not the same substance and do not act with the same specificity.
Regulation. One is a prescription medicine. The other is a cosmetic, which by definition may not be sold as a treatment for anything.

If a page describes a cream as an alternative to a medical procedure, you have learned something about the brand rather than about the ingredient. Actual muscle activity and the lines it produces are covered in what causes wrinkles.

The delivery problem, which is the real one

Set the marketing aside and one genuine limitation remains for the entire category.

Peptides are water-loving and comparatively large. The outer layer of your skin is built to refuse exactly that kind of molecule, and it does not evaluate your ingredient list before deciding. Much of the supporting laboratory work is done on cells, where the barrier is not part of the experiment at all.

This is not an argument against peptides. It is an argument for taking the delivery question seriously instead of pretending it is solved, which is the subject of why your serum is not absorbing.

It is also why re:tones sells both halves of a system. The device opens temporary channels through that outer layer, and the ampoule is released at the moment the needle meets skin, so the formula and the road in arrive together. That mechanism is set out on the science page. It is a description of what the device does, not a promise about your face.

The container follows from the same logic. You are applying to a barrier that is briefly open, so the ampoule is crimp-sealed medical glass you open yourself rather than a pump that meets air and fingertips daily.

How to read a peptide product in one minute

Find the specific name. Acetyl hexapeptide-8 and copper tripeptide-1 are ingredients. Peptide complex is a category.
Look at its position. Near the top is a warning. Somewhere in the middle is normal. Immediately after the preservatives is decoration.
Check the unit. A figure in ppm usually refers to the peptide. A large percentage usually refers to a diluted solution.
Ignore the injectable language. It tells you nothing about the formula.
Ask what carries it in. No brand prints this number, and it is the one that decides everything.

Frequently asked questions

How much peptide should a product contain?

For a named peptide such as acetyl hexapeptide-8, hundreds of parts per million is a normal working level, which is a few hundredths of one percent. Signalling molecules act at low concentrations by design. A large advertised percentage usually refers to a pre-diluted trade solution rather than to the peptide itself.

Why is a peptide high on the ingredient list a bad sign?

Because ingredient lists are ordered by weight. A peptide used at a few hundred parts per million belongs low on that list. When it appears near the top, what is high on the list is usually the water and glycerin the raw material was supplied in, not the active molecule.

Do peptides work as well as retinol?

They are different categories with different amounts of evidence behind them, and comparing them as if one replaces the other is not useful. Retinoids are the better evidenced topical option for visible ageing and also the more irritating. Peptides are generally comfortable to wear, and the open question for them is delivery.

Can I use peptides with vitamin C, retinol or acids?

Generally yes, and most routines that contain peptides contain other actives too. A common arrangement is vitamin C in the morning and peptides in the evening, with a retinoid introduced slowly on separate nights. If a needling session falls in the same week, the retinoid needs its own gap. Add one new product at a time so any reaction has an obvious cause.

Does collagen in a cream add collagen to my skin?

No. The collagen molecule is far too large to cross the outer layer of skin, so a collagen cream sits on the surface as a humectant and a film. Peptides are interesting for a different reason, which is that they may act as signals rather than as raw material.

Is acetyl hexapeptide-8 the same as an injectable treatment?

No. An injectable is a prescription medicine placed into muscle by a clinician. Acetyl hexapeptide-8 is a cosmetic ingredient applied to the surface of the skin, and cosmetics may not be sold as treatments for anything. Any page drawing that comparison is selling rather than explaining.