Toenail fungus, or onychomycosis is a condition in which a common fungus found in the environment invades the nail bed, leading to a yellowing, and thickening of the nail. Although anyone can acquire this infection it is more common in the elderly, and people with chronic medical conditions. Additionally, the same or different kinds of fungus can affect the fingernails of people who work in warm, moist environments (ex. bartenders and dishwashers) as well as those whose immune systems are compromised.