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All You Need to Know About Peptides

what are peptides

There’s been a lot of buzz around peptides on social media and it would be easy to write them off as another viral TikTok trend. But peptides in skincare have an extensive history in this space and some really cool science behind them too.

The Structure of a Peptide

Peptides are composed of strings of amino acids. An easy way to visualize this is to think of Lego blocks. Our little Legos are just amino acids by themselves but when the end of one “cube” attaches to another “cube”… voila, we have a peptide!


For the science nerds: the more technical explanation is that the amino end of one amino acid reacts with the carboxy end of another to form a peptide bond, linking the amino acids into a peptide. These bonded amino acids are called “residues” as they’re left behind after a dehydration synthesis reaction occurs and a molecule of water is released, ending with two linked amino acids. Additional amino acids can be added onto the peptide chain through the formation of more of these peptide bonds - also called amide bonds. 

The Function of a Peptide

In terms of cosmetic applications, it’s the bioactive peptides that we want. To put it simply, “bioactive” just means that it has the potential to interact with our living organs – like skin. (There are plenty of peptides that aren’t bioactive, so if you put them on your skin, they’d just sit there.) These bioactive peptides are the ones involved in cellular processes but in order to be biologically active, the sequence of amino acids (the order of those blocks) is very important.  When the right peptides are used in skincare, they have the ability to positively impact the function of our skin.

It’s also important to note that the term “peptide” covers a very broad category of molecules. Peptides can be hormones like insulin, neurotransmitters like endorphins, antimicrobial peptides called defensins, and even growth factors. In skincare, there are a few main categories of bioactive peptides.

Getting back to our Lego analogy, two connected amino acid “blocks” would be called a dipeptide while three blocks would form a tripeptide. Some other terms you’ll hear is oligopeptide (up to 10 amino acids) and polypeptide (10 or more amino acids). A polypeptide with more than 50 amino acids usually just gets lumped in as a protein.

Speaking of which, if you’re familiar with amino acids being the building blocks of proteins then you may be wondering… what exactly is the difference between a peptide and protein? If a peptide is our string of Legos, a protein would be connecting several of those strings and twisting them into a 3D structure. Proteins deserve their own blog as there is a lot that goes into their structure - the specific sequence of the amino acids, the coiling of the peptide chains, the bonds holding the protein in its shape, and more.  Let’s begin with just peptides so we’re not biting off more than we can chew.

Types of Peptides

The history of peptides in skincare goes all the way back to 1973 with Dr. Loren Pickart’s research on copper peptides. Later in 2001, the launch of Argireline and all the buzz around the “Botox in a bottle” alongside the release of Matrixyl really cemented the place of peptides in skincare. Since then, peptide technology has become quite sophisticated and we have four categories of peptides commonly used in cosmetics.


Signal peptides

These peptides are like floor managers in a factory, telling your skin cells what to do and when. The popular ones are mostly helpful for skin aging and may work by signaling fibroblasts to produce more collagen and elastin, or by triggering skin cells to divide and migrate to where we want them.

Examples: Palmitoyl Pentapetide-4 (Matrixyl®), Palmitoyl Tripeptide-5 (Syn®-Coll), Copper Palmitoyl Heptapeptide-14

Carrier peptides

Carrier peptides are like taxis, transporting unique ingredients to where they’ll be put to the best use. The first ones were used to carry important trace elements like copper into the wounded tissue for better healing.

Examples: Copper Tripeptide-1, Heptapeptide-15 Palmitate

Neurotransmitter inhibitor peptides

Skincare peptides in this category are designed to inhibit the release of acetylcholine at the neuromuscular junction. Essentially, the goal is to stop facial muscles from getting the signal to contract, which smooths dynamic wrinkles.

Examples: Acetyl Hexapeptide-3 (Argireline), Pentapeptide-18 (Leuphasyl), Dipeptide Diaminobutyroyl Benzylamide Diacetate (Syn-Ake)

Enzyme inhibitor peptides

These peptides stop certain processes from occurring rather than initiating them. For example, preventing enzymes from breaking down collagen or inhibiting inflammatory processes.

Examples: silk fibroin peptides, soybean derived bioactive peptides 

Peptide Formulation 

If you’ve read this far, you’re likely beginning to see why peptides generate a lot of excitement. Having peptides come in and whip our skin into shape like a personal trainer for skin sounds like a dream come true.

But there are 2 important considerations to discuss: 1) getting the peptides into the skin and 2) which peptides have research behind them.

#1 Skin Penetration 

Our skin is literally designed to keep things out. Great for keeping the bad things out, not so great when we’re trying to get the good stuff into the skin. Luckily, topical medications run into many of the same obstacles so we have a lot of research on drug delivery to guide us.


Routes into the Skin

  • Transcellular pathway. A very selective route as ingredients must pass straight through the skin cells, usually restricted to small water-soluble ingredients
  • Intercellular pathway. Larger, oil-loving molecules can use this route to diffuse through the lipids between skin cells.
  • Transappendageal pathway. While least common, some ingredients are able to penetrate via the hair follicles and glands.

Okay, so where do peptides fit in? That’s the problem… Many peptides don’t meet the criteria needed to utilize these penetration routes into the skin. The earliest iteration of Argireline is a great example as it’s hydrophilic (water loving) but too large to pass through the transcellular pathway. Even worse, its charged state further hinders penetration as our skin barrier is negatively charged. Have you ever tried to force two magnets together with the same polarity and noticed they repel each other? That’s essentially what’s happening here.

Because of this issue, there’s been a heavy focus on how to get peptides to where they’ll be most useful within our skin.

Methods of Enhancing Penetration

  • Delivery systems including encapsulation in vehicles like nanosomes or liposomes
  • Modification of the ingredient. For example, attaching a fatty acid to the peptide.
  • Chemical penetration enhancers like alcohol, glycerin, urea, surfactants.
  • Physical penetration enhancers like microneedles, iontophoresis, and ultrasound.
  • Combining methods, like enhancing penetration of nanoparticles with ultrasound.

#2 Peptide Research

The other consideration with peptides is the extent of the research. We want to know if the peptide can get into the skin, what concentration and other formulation specifics are needed, how the peptide works, and if research showed that they improve our skin.

What to look for in peptide research:

  • Systematic reviews, meta analyses, and controlled clinical trials and studies
  • Is the study well designed? i.e. controlled to limit variables, collects objective data
  • How many subjects are there?
  • How long was the duration of the study?
  • Who funded the study?
  • How did they assess the study results?
  • Do the authors reference other research and acknowledge limitations in the study?
  • Are the findings replicated and reproduced in subsequent studies?

If you’re not one to dive into the research, that’s okay! Another great option is to look for peptides in a product you’ll be using anyway - ideally with other research backed ingredients like niacinamide, panthenol, or even retinoids. It doesn’t have to just be a peptide serum either, a peptide moisturizer is an easy way to introduce the benefits of peptides without complicating your routine. 

Stratia’s Peptide Powerhouse: Interface

Everything we’ve been discussing about peptides ultimately leads to our own peptide product. Our founder Alli spent years developing a peptide cream that would align with Stratia’s brand philosophy and offer an innovative and unique peptide product to the market. More recently, Interface also got a makeover and supercharged its signal peptides.

First, let’s chat about Interface as a peptide moisturizer. In cosmetics, a vehicle is the inactive cream, balm, or serum that active ingredients are added to and together they make the finished formulation. Interface uses a gel cream vehicle for the peptides and packs in high-quality humectants alongside emollients and occlusives that aren’t heavy on the skin, resulting in a light but intensely hydrating product. 

The challenge with peptides is not only selecting the right ones, it’s getting them to where they’ll function most effectively… and Interface does this with a delivery system that is truly groundbreaking. Copper Palmitoyl Heptapeptide-14 is a signal peptide that stimulates the production of collagen and elastin - but it needs to reach the fibroblasts to work. To achieve that, it’s been placed in a capsule made from glycolic acid/lactic acid copolymer to get it into our skin.

But we didn’t just stop at a delivery system. Simple encapsulation helps with skin penetration but it’s like trying to deliver a package without knowing where you are and hoping you’ll stumble across your destination. By anchoring a targeting peptide called Heptapeptide-15 Palmitate to the capsule, we’re giving our “car” the GPS needed to drive right to our fibroblasts and deliver our precious cargo. 

This concludes our peptide post but there’s more to come! In honor of the 5 different growth factors we’ve added to Interface, Part 2 is going to dive into the science behind them and answer all your collagen peptide questions.