Candida albicans is a type of yeast that normally lives in our mouth, skin, and gut without causing any trouble. But when our immune system is weakened or our oral environment is disturbed, Candida albicans can change its shape and invade our tissues and organs, causing infections called candidiasis. Candidiasis can be fatal if not treated. Candida albicans can also stick to the plaque on our teeth and gums, and cooperate with bacteria such as Streptococcus mutans to cause tooth decay or caries.