Peptides

Peptides are short chains of amino acids, the same building blocks that make up proteins. The distinction is simply one of length: string enough amino acids together and you have a protein such as collagen; keep the chain short, typically between two and around fifty, and you have a peptide. That difference in size is what makes them useful on skin, because proteins are far too large to go anywhere and peptides are not.

The word covers a very broad category rather than a single ingredient, which is the main reason it can be confusing on a label. Palmitoyl Tripeptide-1, Palmitoyl Tetrapeptide-7, Acetyl Hexapeptide-8, Copper Tripeptide-1 and Palmitoyl Pentapeptide-4 all appear under the peptide heading and behave quite differently from one another. Saying a product contains peptides is a little like saying a meal contains vegetables.

Broadly, they are grouped by what they appear to do. Signal peptides are associated with the skin’s production of structural proteins. Carrier peptides deliver trace elements such as copper. Enzyme-inhibiting peptides interfere with the breakdown of existing structure. Neurotransmitter-inhibiting peptides are the group marketed in connection with expression lines.

The palmitoyl prefix that appears so often is a fatty acid attached to the chain to help it pass through the skin’s lipid layer, since peptides are water-loving and the barrier is not.

They are used at very low percentages, usually a fraction of a percent, and appear mainly in serums, eye products and moisturisers aimed at the look of firmness and fine lines. They are notably well tolerated, which is why they are often recommended for skin that reacts badly to retinoids.

Peptides act as messengers rather than as raw materials. When the skin’s supporting structure is damaged, collagen breaks down into characteristic short fragments, and the presence of those fragments is one of the signals the skin uses to recognise that repair is needed. Many cosmetic peptides are designed to resemble those fragments. Applied to skin, they appear to prompt a repair response without any damage having occurred, which is the central idea behind the whole category.

Different groups take different routes. Signal peptides encourage cells to produce more of the structural proteins that keep skin looking firm. Carrier peptides deliver trace elements the skin needs for those processes, with copper being the most familiar example. Enzyme-inhibiting peptides work from the other direction, slowing the enzymes that break existing collagen down. Neurotransmitter-inhibiting peptides interfere in a small way with the signalling between nerves and facial muscles, which is the basis for their association with the look of expression lines, though the effect of a topical product is modest and not comparable to a clinical treatment.

Two honest caveats sit alongside this. Getting a peptide through the barrier in a useful state is genuinely difficult, which is why delivery systems and the fatty acid attachments matter so much. And the evidence base is uneven: it is strong for some specific peptides and thin for others, so the category as a whole is less uniformly well supported than something like retinol or vitamin C. Peptides are best regarded as a gentle, supportive addition rather than a replacement for the better-established actives.

Peptides are among the least demanding ingredients to use, which is a large part of their appeal.

• When: morning and night. There is no tolerance to build, no sun sensitivity and no need for breaks.
• Order in the routine: after cleansing and any watery layers, before moisturiser. If a peptide serum is the thickest thing you use, it goes last before SPF.
• Leave-on only. A peptide cleanser is money spent on something you rinse straight off.
• Look for named peptides, not just the word on the front. A specific INCI name such as Palmitoyl Tripeptide-1 tells you what you are actually buying.
• Pairs well with: niacinamide, hyaluronic acid, ceramides, squalane and antioxidants. Peptides are frequently used to support skin that is also on a retinoid.
• Keep apart from strong acids in the same layer. A low-pH environment can affect some peptides, so use exfoliating acids at the other end of the day rather than directly underneath.
• Copper peptides are a special case and are best used on their own rather than layered with vitamin C or acids.
• Sunscreen still does the heavy lifting. Peptides support the skin’s structure; daily SPF is what protects it.

Expect a gradual effect on the look of firmness and fine lines over two to three months, and treat any promise of dramatic short-term change with scepticism.