There are several factors that can increase your risk of developing thrush.

Age

• Newborns and infants don't have fully developed immune systems, which increases their risk of developing infections, including thrush.
• Newborns are also in the process of developing a healthy balance of bacteria and fungi in their mouths. If this balance is upset, the child may develop thrush.
• Older adults, especially those who have serious health problems, are more likely to develop thrush because their immune systems are likely to be weaker.

Behavior

• The yeast that causes thrush can be spread by oral sex.
• Heavy smoking can lower the body's ability to fight off infections, making thrush more likely to develop.

Other conditions

• False teeth (dentures), braces, or a retainer that irritates the mouth make it hard to keep the mouth clean and can increase your risk of developing thrush. An unclean mouth is more likely to develop thrush than is a clean mouth.
• People with a weakened immune system, such as those who have diabetes or human immunodeficiency virus (HIV) or who are undergoing chemotherapy, have an increased risk for developing thrush.

Medications

Some medications can allow the fungus that causes thrush to grow uncontrolled.

• Antibiotics, especially those that kill a wide range of organisms (broad-spectrum antibiotics), such as tetracycline
• Birth control pills (oral contraceptives)
• Medications that weaken the body's immune system, such as corticosteroids

Environment

Exposure over time to certain environmental chemicals, such as benzene and pesticides, can weaken the body's immune system, increasing your risk for developing infections, including thrush.