A yeast called Candida albicans causes thrush. Yeast is a type of fungus that can be found in a person’s intestines, mouth or skin. The body normally regulates the amount of yeast it has, but in some cases yeast can grow uncontrolled.

Thrush is commonly found in infants during the first few months of life. Young children have less fully developed immune systems than adults, so their bodies are less able to control the normal balance of yeast and bacteria. Newborn babies sometimes develop thrush after birth when their mothers have vaginal yeast infections at the time of delivery. In addition, babies who take antibiotics may kill off the bacteria in their bodies that normally control yeast.

Nursing mothers who take antibiotics are also at increased risk for developing thrush. In addition, a baby with oral thrush can infect the mother’s nipple during breastfeeding. Pregnancy itself can also cause thrush because the higher levels of the hormones estrogen and progesterone alter the balance of bacteria in the woman’s mouth and vagina.

Certain diseases may increase the risk of thrush in children. For example, chronic mucocutaneous candidiasis are a group of rare disorders that typically affect children younger than age three. These disorders are marked by chronic Candida infection of the mouth, fingernails and skin of the scalp, trunk, hands and feet.

Additional factors that can increase the risk of thrush in a nursing mother or her child include a mother’s high sugar diet or low resistance to disease due to fatigue or other health issues.

Other factors which can increase the likelihood of developing oral thrush in general include:

• Diabetes mellitus
  
  
• HIV/AIDS and other diseases that weaken the immune system
  
  
• Cancer
  
  
• Mononucleosis and other viral infections
  
  
• Certain medications, such as antibiotics, corticosteroids, birth control pills and drugs to suppress the immune system
  
  
• Chemotherapy
  
  
• Dry mouth (xerostomia)
  
  
• Irritation from partial plates or dentures
  
  
• Old age
  
  
• Poor health
  
  
• Smoking