Ingredient dictionary

Threonine

Threonine is an amino acid, one of the small building blocks of proteins. In skincare and haircare it mainly helps hold water and keep skin or hair soft. It is on the label of 19 products in our library. Checked against our library November 6, 2026.

What Threonine does

Helps skin and hair hold water
Softens hair and makes it easier to comb
Gives a smooth, comfortable feel to formulas

Threonine is an amino acid, a small molecule that joins with others to form proteins. Most of the threonine used in cosmetics is made by fermentation, a process similar to how some food ingredients are made. Ingredient makers grow microbes in sugar-based mixtures, which then produce the amino acid.

In formulas, threonine works as a conditioning agent. It helps attract and hold water on the skin or hair, which can leave surfaces feeling smooth and supple. It is light and water-soluble, so it blends easily into lotions, serums and rinse-off products without a heavy or greasy feel.

Good for

Good for people who want a light, everyday moisture boost in cleansers, serums, moisturizers, conditioners and styling products.

Frequently asked questions

Is threonine good for skin?

Threonine is mainly used as a conditioning ingredient. It helps skin hold water, which can leave it feeling soft and supple. It is one of many amino acids in moisturizers and serums, and it works alongside other ingredients.

Is threonine safe for sensitive skin?

Threonine is generally well tolerated and is not known as a common irritant. Because it is a natural building block of proteins, it is usually a low-fuss ingredient. If your skin reacts to any new product, stop using it and check with a dermatologist.