Consisting of live microorganisms that are beneficial to the health, probiotics are mostly found in fermented foods like yogurt, soy yoghourt and kefir. Probiotics are similar to the beneficial microorganisms found in the human gut. They are also called "friendly bacteria" or "good bacteria." Probiotics are available to consumers mainly in the form of dietary supplements and foods.

Taking probiotics as supplements provide many health beneifts including increased protection against many upper respiratory tract infections (URTI) including the common cold.