Yeast is a rich source of beta-glucan, an antioxidant. There is limited information about how Saccharomyces cerevisiae, in particular, may provide benefits in skincare. However, it’s marketed as a being a great ingredient that brightens, fades sunspots and age spots, evens skin tone, controls cell turnover and oiliness.

Beta-glucan can be derived from yeast or oats. It has some antioxidant properties and is a strong anti-inflammatory agent. It is considered an excellent ingredient for reducing redness and other signs of sensitive skin.

Live yeast-cell derivatives have been shown to stimulate wound healing but there isn’t much research on this.

Much of what is known about yeast’s effects for skin is theoretical, and concerns yeast’s tissue-repair and protective properties or yeast’s antioxidant properties.

As a skin-care ingredient yeast has potential, but what its function may be or how it would affect skin is not fully understood.

Pitera (Saccharomycopsis Ferment Filtrate) has some in vitro research demonstrating it has antioxidant ability.

Great reads on yeast extract

Inhibition of inflammatory nitric oxide production and epidermis damages by Saccharomycopsis Ferment Filtrate.
Trophic effect of a methanol yeast extract on 3T3 fibroblast cells.
Journal of Drugs in Dermatology, February 2007, pages 167-170
Free Radical Biology and Medicine, February 2001, pages 393-402
Peptides from live yeast cell derivative stimulate wound healing.
Global Cosmetic Industry, November 2001, pages 12–13
Archives of Surgery, May 1990, pages 641–646
Nature Genetics, December 2001, pages 426–434
FUNGAL POLYSACCHARIDES
Many microorganisms such as bacteria and fungi possess so-called capsules made of polysaccharides, which protect these microorganisms from environmental insults and host immune defenses. Used in cosmetics to hold skin moisture.