Soy Protein

What Is Soy Protein in Skincare?

Soy protein is the protein portion of the soybean (Glycine soja or Glycine max), used in skincare either whole, as hydrolyzed soy protein (broken into smaller amino acid chains), or as part of active blends. On the skin it forms a light, smoothing film that helps hold in moisture and gives an instant look of firmness. Some soy ingredients also carry natural compounds, such as soybean trypsin inhibitor, that researchers have studied for their effect on the look of uneven tone.

EWG Skin Deep rating for Soy Protein

Soy Protein Quick Facts

How Soy Protein Works on the Skin

Moisture and a smoothing film

Proteins and their hydrolyzed peptides are too large to sink deep into the skin. Instead they sit on the surface, bind water, and dry into a thin, flexible film. That film helps reduce water loss, makes the skin feel softer, and gives a temporary look of tighter, smoother skin. This is why soy protein is popular in eye creams and firming serums.

Soy and the look of even tone

Fresh, non-denatured soy contains two proteins, soybean trypsin inhibitor and Bowman-Birk inhibitor, that block certain skin enzymes. In a 2001 paper from Johnson and Johnson researchers in the Journal of Investigative Dermatology, Paine and colleagues reported that soymilk, STI, and BBI reduced the way skin cells take up pigment from melanocytes, through a receptor called PAR-2, in lab and animal models. That is why soy extracts are used in products for the look of uneven tone.

What the clinical study measured

In a 12-week, double-blind, vehicle-controlled study, Wallo, Nebus, and Leyden (2007) had 65 women with moderate facial photodamage use either a soy moisturizer containing non-denatured STI and BBI or the same moisturizer without soy. The soy moisturizer was significantly better at improving the look of mottled pigmentation, blotchiness, dullness, fine lines, texture, and overall tone, with differences seen from week 2 for most measures. This study tested a specific non-denatured soy extract, not hydrolyzed soy protein, so results apply to that type of ingredient.

How to Use Soy Protein in Formulas

• When to add: add hydrolyzed soy protein to the water phase or the cool-down phase below 40°C (104°F). Non-denatured soy extracts must stay cool, because heat destroys the STI and BBI activity.
• pH: stable in the typical facial range of pH 5 to 7.
• Pairings: soy protein works well with hyaluronic acid, wheat protein, and amino acid sequences such as Argireline in eye products.
• Using Regu-Age: add Regu-Age at the top of its 2 to 5% range: 45 drops (5%) per fluid ounce of eye cream or serum, at the house rate of 9 drops = 1%.
• Preservation: proteins feed microbes, so water-based products need a broad-spectrum preservative.
• Storage: keep sealed and cool; refrigerate concentrated boosters after opening if the label says so.

Who Soy Protein Suits

Soy protein suits dry, mature, and dull skin and is especially useful around the eyes, where a light firming film helps the area look smoother and more rested.

Sensitive skin and allergies: anyone with a soy allergy should avoid soy protein skincare and ask their doctor first. For sensitive skin, patch test on the inner arm for 24 hours and start at the lowest rate, such as 2% (18 drops per fluid ounce) for Regu-Age, then work up.

Frequently Asked Questions

What does soy protein do for skin?

Soy protein binds moisture and forms a smoothing film, helping skin look softer, firmer, and more hydrated. Some soy extracts also help the look of uneven tone.

Is hydrolyzed soy protein good for skin?

Yes. Hydrolyzed soy protein is a gentle humectant and film former used in serums, creams, and eye products. It gives a temporary look of smoother, tighter skin.

Is hydrolyzed soy protein the same as soy extract?

No. Hydrolyzed soy protein is broken into smaller amino acid chains for moisture and film forming. Non-denatured soy extract keeps its natural enzyme-blocking proteins, which are the ones studied for tone.

Does soy help with dark spots?

Non-denatured soy extracts have been studied for the look of uneven tone. In a 12-week study of 65 women, a soy moisturizer improved the look of mottled pigmentation and blotchiness compared with the plain moisturizer.

Does soy in skincare contain estrogen?

Whole soy extracts can contain isoflavones, plant compounds sometimes called phytoestrogens. Purified and hydrolyzed soy proteins contain little to none.

Can people with a soy allergy use soy skincare?

Anyone with a soy allergy should avoid soy protein skincare and ask their doctor first. Proteins are the part of soy most linked to allergy.

Shop Soy Protein Skincare

Add Regu-Age Eye Serum Booster to your eye cream, or try soy protein ready-made in the Uplift Eye Cream. To learn how proteins compare with peptides, read the difference between peptides and proteins in skincare.

Sources

• Wallo W, Nebus J, Leyden JJ. Efficacy of a soy moisturizer in photoaging: a double-blind, vehicle-controlled, 12-week study. Journal of Drugs in Dermatology. 2007;6(9):917. JDD article (65 women, 12 weeks)
• Paine C, Sharlow E, Liebel F, Eisinger M, Shapiro S, Seiberg M. An alternative approach to depigmentation by soybean extracts via inhibition of the PAR-2 pathway. Journal of Investigative Dermatology. 2001. (lab and animal models)
• Skin Perfection, Regu-Age Eye Serum Booster product page: 2 to 5% usage rate.

These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.

About the Author
Written by Kari Thomas, cosmetic formulator and founder of Skin Perfection.