Threonine is an alpha amino acid that is used as a building block during the production of proteins. It is considered to be an essential amino acid, which means that it must be obtained from the diet since the human body cannot produce it. Foods high in threonine include cottage cheese, fish, meat, and sesame seeds.

It is thought that threonine and other amino acids used in skin care products can assist the skin in making important proteins, such as collagen and elastin. Collagen is important for skin strength, while elastin is important for skin elasticity. Both collagen and elastin levels in the skin decrease with age. The skin needs essential amino acids like threonine to generate these proteins and new skin cells. Deficiency in essential amino acids will result in skin that appears visibly dry and thin. Therefore, topical application of ingredients that stimulate the production of  collagen and elastin, such as threonine, may help to decrease signs of aging and improve the overall appearance of skin. Threonine also improves skin hydration because amino acids in the skin work together with aquaporins (the body’s water transport system) to move moisture throughout skin.