Oral thrush is not related to oral hygiene; instead, it results from an imbalance of organisms in the mouth due to a compromised immune system or certain medications, according to the Mayo Clinic. Although anyone can get oral thrush, infants and the elderly are more likely to be affected.
Oral thrush is a fungal infection caused by Candida albicans and is normally present in the mouth, but an overgrowth can lead to symptoms of oral thrush such as white lesions on the tongue, as stated by the Mayo Clinic. Although the immune system normally maintains the balance of viral, bacterial and fungal organisms in the body, certain conditions can disrupt the body's protective mechanisms. Oral thrush may be an early sign of HIV/AIDS, and individuals with diabetes mellitus may be more likely to develop oral thrush due to excess sugar in the saliva.
Both cancer and related treatments such as chemotherapy and radiation therapy may make a patient susceptible to Candida infections, as stated by the Mayo Clinic. Women with vaginal yeast infections may pass a Candida infection on to a newborn, resulting in oral thrush in the infant. Antibiotics, corticosteroids, conditions that cause dry mouth and the use of dentures may also put individuals at risk of developing oral thrush.