The natural moisturizing factor in human skin. TwinLab Na-PCA is a Ph-balanced, concentrated solution of the sodium salt of pyrrolidone carboxylic acid, the natural moisturizing factor found in human skin. Na-PCA is synthesized from glutamic acid, a nonessential amino acid. The skin contains natural moisturizers, the most important being Na-PCA. Old skin contains only about half the amount of Na-PCA as that found in young skin. The ability of skin to hold moisture is directly related to its Na-PCA content. It is water, and not oil, that keeps skin soft and supple. Na-PCA pulls water out of the air, moisturizing the skin, improving its appearance, and giving it a moist and youthful glow. This is not a cosmetic cover up; it is a physiological correction of an age-related deficiency state. Hypo-allergenic.