Yeasts are eukaryotic microorganisms classified in the kingdom Fungi, with 1,500 species currently described[1] (estimated to be 1% of all fungal species).[2] Yeasts are unicellular, although some species with yeast forms may become multicellular through the formation of strings of connected budding cells known as pseudohyphae, or false hyphae, as seen in most molds.[3] Yeast size can vary greatly depending on the species, typically measuring 3–4 µm in diameter, although some yeasts can reach over 40 µm.[4] Most yeasts reproduce asexually by mitosis, and many do so by an asymmetric division process called budding.