Candida , the yeast that causes thrush, is normally present in small amounts in the mouth and on other mucous membranes. It usually causes no harm. But when conditions are present that let the yeast grow uncontrolled, the yeast invades surrounding tissues and becomes an infection.
Thrush is most commonly caused by the yeast Candida albicans. Less frequently, other forms of Candida can lead to thrush.
There are many types of bacteria in your mouth that normally control the growth of Candida. Sometimes a new type of bacteria gets into your mouth and disrupts the balance of the organisms already there, allowing Candida to overgrow. Health conditions and other things may also be involved.
How thrush spreads
The yeast that causes thrush can pass from one person to another in different ways.
- A newborn can get thrush during birth, especially if his or her mother had a vaginal yeast infection during labor and delivery. Newborns and infants have an immature immune system and have not fully developed a healthy balance of bacteria and yeast in their mouths. Because of this, thrush is common during the first few months of life.
- In otherwise healthy toddlers and older children, thrush is usually not contagious. But a child with a weakened immune system may get thrush by sharing toys or pacifiers with a child who has the infection. A child who has thrush spreads the thrush yeast onto anything the child puts in his or her mouth. Another child may then get thrush by putting a contaminated object into his or her mouth.
- Adults who wear false teeth (dentures) are at a higher risk for getting thrush and spreading it to others. A person can get thrush by spreading the yeast from their hands to their dentures. And a person with dentures may spread the yeast by handling their dentures and then contaminating an object that another person touches or puts into his or her mouth.