The mouth is dry. A fungus called Candida albicans. This may upset the natural balance of organisms in the mouth and allow thrush to develop. Newborns may acquire the infection during passage through the birth canal, especially if the mother has a vaginal yeast infection. Thrush appears within hours or up to 7 days after birth.
Older persons develop thrush because of lower natural resistance.
Illness that has lowered resistance. Irritation from dentures. Immunosuppression due to illness or drugs. Avoid unnecessary antibiotics. Medical history and physical exam by a doctor.