Do you know what our largest organ is? No, not the intestines, stomach, liver, nor brain. It’s our skin! Skin covers almost all of our body and plays an important barrier role in keeping viruses and bacteria out of us and our internal organs in.

But what exactly is skin made of? Like all of our other cells, skin is made of proteins, lipids, and nucleic acids. However, one protein in particular is super abundant in skin and helps it function properly: collagen (Figure 1). In fact, collagen makes up nearly a third of the total protein content in our bodies (Deshmukh et al., 2016)!

Numerous cosmetic and aesthetic treatments use proteins and peptides to keep our skin healthy and to provide a youthful appearance. Many of these applications work by ramping up the production of collagen in our skin cells, or by adjusting the interactions between skin cells and our nervous and immune systems.

Collagen triple helix. Different colors indicate distinct collagen strands

Figure 1. Collagen triple helix. Different colors indicate distinct collagen strands (PDB: 1BKV).

Article Table of Contents:


Growth Factors




Collagen fillers



You have likely seen ads for skincare products and lotions that promise to prevent aging and keep your skin looking young and healthy. Maybe you use these lotions yourself. Have you ever wondered or investigated what these concoctions contain?

The active ingredients in many cosmetics include proteins such as growth factors and peptides.

Growth Factors

Growth factors are proteins that bind to the outside of cells to convey specific information to these cells. In the context of cosmetics, growth factors bind to skin cells to promote:

  • wound healing to reduce the appearance of scars.
  • production of collagen to give skin a firmer and younger look.
  • growth of blood vessels to enhance distribution of endogenous growth factors to skin.

Your body naturally uses growth factors to maintain skin health. However, growth factors often dwindle as we age, so providing your skin with an extra boost of growth factors can enhance these processes.


Peptides are used in a number of cosmetics including anti-aging skin products. These peptides fall into distinct functional classes that:

  • inhibit neurotransmitters.
  • stimulate collagen production in skin cells.
  • prevent inflammation.

For example, palmitoyl pentapeptide inhibits neurotransmitters, copper tripeptide inhibits inflammation, and acetyl hexapeptide stimulates the production of collagen (Figure 2).

Examples of cosmetic peptides.

Figure 2. Examples of cosmetic peptides.

Cosmetics usually contain multiple distinct peptides from each of these classes, resulting in mixtures of tens to hundreds of different peptides.


If you are up to date on the red carpet gossip, you probably know which movie stars are the latest to get Botox® or collagen fillers. Both of these treatments are examples of aesthetic dermatology.

Aesthetic skin treatments are intended to enhance skin appearance outside of the context of any kind of skin disease.


Botox® is a popular aesthetic treatment for aging and wrinkling skin. The active ingredient is a protein from the pathogen Clostridium botulinum, which causes botulism. Botulism attacks nerve cells and causes difficulty breathing, muscle paralysis, and even death if not treated properly.

Low doses of one C. botulinum neurotoxin, onabotulineurotoxin A (Figure 3), are locally injected in Botox® treatments to temporarily paralyze nerves within face muscles. Through this mechanism Botox® reduces wrinkles. However, new toxin must be reinjected every few months to maintain the wrinkle-free appearance due to its temporary nature.

Onabotulineurotoxin A, the active neurotoxin in Botox® molecular rendering

Figure 3. Onabotulineurotoxin A, the active neurotoxin in Botox® (PDB: 3BTA).

Although most commonly known for its aesthetic applications, Botox® was originally developed as a medical treatment and is still used for a number of diseases involving spastic or misaligned muscles including:

  • strabismus
  • blepharospasm
  • cervical dystonia
  • axillary hyperhidrosis
  • incontinence due to hyperactive bladder

Onabotulineurotoxin A is purified from C. botulinum cultures by dialysis and multiple acid/salt precipitations (Lamanna et al., 1946; Allergan Pharmaceuticals Inc., 2004). Dialysis separates onabotulineurotoxin A from smaller proteins and small organic molecules such as metabolites and nucleotides.

Most proteins precipitate in acidic pH and high concentrations of salts. Yet the pH, type of salt, and concentration of salt at which individual proteins precipitate varies. These unique properties allow scientists to perform a series of intentional protein precipitations to purify their protein of interest away from other cellular proteins.

This precipitation technique is used to purify onabuotulineurotoxin A away from other C. botulinum secreted proteins by performing a series of acid and salt precipitations using a combination of different pH values, and different types and concentrations of salts (Lamanna et al., 1946).

Since Botox® is a toxin, you may be wondering how it is dosed to give the desired effects on skin without accidentally poisoning people. Each batch of Botox® purified as described above is tested and given an activity “unit,” where the unit corresponds to the median lethal dose of that batch when injected into mice. For this reason, Botox® from different manufacturers, and even different batches from the same manufacturer, are not exchangeable.

Since we are much larger than mice, anywhere from 2 to 50 units of Botox® are injected, with the exact amount dependent on the nature of the injection site. For instance, 2 to 6 units are injected into the chin whereas 25-50 units are injected into the neck (Green, 2014).

Proper injection by a skilled healthcare professional minimizes the occurrence of side effects, which are usually mild and localized to the injection site.

Collagen fillers

Image of an injection by the lips for collagen fillers which are made of purified proteins

Figure 4. Collagen injections are thought to be more effective and deeper penetrating than creams.

Collagen injections, also known as fillers, are another aesthetic skin treatment thought to give skin a fuller and more youthful look. Exogenous collagen can be injected deeper than surface creams reach, which some feel gives skin a plumper appearance.

The collagen used in fillers is purified from animal skins such as cowhide. Traditionally, harsh acid or base treatments were used to release collagen from the cowhide. However, researchers later discovered that proteases could cut collagen off of the cowhide instead of the acid and base treatments. This alternative process is more environmentally friendly as it eliminates toxic waste generation.

Collagen is the most abundant protein in these extractions and is additionally purified by:

  • intentional protein precipitation using salt and acid.
  • ion-exchange chromatography.

Ion-exchange chromatography uses the intrinsic charge of a specific protein, collagen in this case, to purify it away from other cellular proteins.

Since animal collagen is used in fillers, a substantial minority of patients develop allergic reactions. An allergy test is performed on a small section of the forearm to try to uncover patients that develop allergic reactions before they develop a major rash on their face.

Over time, the proteases within our bodies will naturally degrade injected collagen. So, the fillers described above are a temporary fix and need to be updated on a monthly to yearly basis to maintain the desired appearance.

However, a recent advance on fillers uses cow collagen in combination with polymethylmethacrylate (PMMA) beads. After our proteases cleave the cow collagen, the inert PMMA beads remain, forming a scaffold that stimulates collagen production and infill from the surrounding skin cells. This longer-lasting formula persists for roughly 5 years and is the most common collagen injection used in the United States (Cockerham and Hsu, 2009).

Let’s wrap up this article on skin care. Hopefully you now know a little more about the powerful proteins that play key roles in cosmetic and aesthetic skin care applications, and how they are purified.


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