Our skin cells, or corneocytes, contain keratin fibers, which are responsible for the “spring back” or elasticity of our healthy and moisturized skin, so it’s vital to keep them hydrated. Proteins are larger molecules composed of amino acids held together by covalent peptide bonds, which account for around 40% of the matter found in the water soluble natural moisturizing factor found in the upper layer of our skin (stratum corneum). Lowered levels of natural moisturizing factor can result in barrier deficiencies and increased transepidermal water loss, which can lead to symptoms of dryness, like a feeling of tightness as well as flaking and cracking skin, and an increase in the appearance of fine lines and wrinkles. 

Cosmetic proteins and amino acids can be derived from so many different ingredients, and every time I go shopping, I see more offered by our suppliers. The most common used to be silk, oat, keratin and soy, but in recent years I’ve seen ones derived from eggs, peas, flowers and milk, to name a few. The lower the molecular weight, the better they will penetrate your hair or stratum corneum to hydrate. The higher the molecular weight, the better they film form and condition as well as conferring a silky, smooth skin or hair feel to whatever you’re making. They have high water holding capacities, meaning all will act as humectants to draw water from the atmosphere to hydrate well regardless of molecular weight. 

As some of these ingredients may be derived from animal products, check the description and INCI of each ingredient if you’re seeking plant derived proteins. 

You’ll find most proteins described as “hydrolyzed” or called “hydrolysates”, which means the chemical bonds have been altered by adding water to create smaller or different molecules with varying molecular weights. They can be water or oil soluble, so check with your supplier to ensure you’re getting the version you want. Most can be used over a wide range of pH levels, and, like our amphoteric surfactants like cocamidopropyl betaine, they tend to be more positively charged or cationic in an acidic product; more negatively charged in alkaline ones. 

Proteins can be modified to include a quaternary or positively charged group to adsorb to your negatively charged hair or skin to condition through a process called substantivity. These proteins tend to be more hydrophobic or water-hating than other proteins, so they will resist removal by water alone and continue conditioning for longer. You’ll see these proteins listed as having “-trimonium” or “-dimonium” in the INCI names, and they’re great inclusions in hair care products like shampoos, and rinse-off or leave in conditioners, as well as body cleansers. 

Adding these ingredients to surfactant based products like facial and body cleansers can prevent protein denaturation and reduce the surfactants’ affinity for skin proteins, both of which can lead to a disrupted skin barrier, increased transepidermal water loss, and dry skin. The more substantive the protein, the more it will increase mildness. As a bonus, they increase foam stability as well as skin feel, adding more slip and creaminess to the lather, which is always lovely. 

Or you could use the proteins as your surfactants. We’re seeing a number of different proteins modified to act as very mild foamy, lathery and bubbly ingredients in facial and body cleansers, as well as specialized no-rinse products, like micellar waters and make-up removers. They may be slightly positively or negatively charged and less irritating than other surfactants. Use them at up to 10% with other surfactants in the heated water phase, or use them as stand alone surfactants to create very mild to gentle cleansers for very sensitive skin. Look for these with INCI names like Sodium Cocoyl Hydrolyzed (silk, oat, soy) Protein. 

Water soluble hydrolyzed proteins and amino acids can be interchangeably used in just about any product with a water phase, but be aware they can dramatically reduce viscosity or ruin the emulsion when used with gels or emulsifiers that don’t work well with electrolytes, like Aristoflex AVC. Oil soluble proteins can be used in anhydrous products or those with an oil phase, and work well with gels with emulsifying capabilities, too. Both types are what we informally call “bug food”, or ingredients that tend to attract more of the microbes that can cause contamination. Ensure you’re using a good, broad spectrum preservative, like liquid Germall Plus or Germaben II, at close to or at to the maximum suggested usage rate, and add them in the heated water phase, when applicable. 

As it seems with every awesome ingredient, there’s a tiny down side: Some proteins and amino acids may have a slightly fishy or earthy smell straight out of the bottle. I can assure you, though, as someone who’s super sensitive to earthy smells, I’ve never noticed it in the final product when used at 2% or lower, even in unscented products I might use on my face.