Lactic acid fermentation is a metabolic process by which glucose or other monosaccharide sugars are converted into lactic acid and energy. There may also be other by-products of this fermentation. The process also works with other sugars, such as sucrose or lactose. Lactic acid bacteria use this process to get energy. Fungi, plants and animals will also use this process, if there is a lack of oxygen. As an example, it occurs in muscle cells. With humans, it occurs if there's too little oxygen in the blood, known as Hypoxemia.