"Oral Thrush in Adults
"There are a number of reasons why this may happen, including:
taking a course of antibiotics, particularly over a long period or at a high dose
taking inhaled corticosteroid medication for asthma
wearing dentures (false teeth), particularly if they don't fit properly
having poor oral hygiene
having a dry mouth, either because of a medical condition or a medication you are taking
smoking
having chemotherapy or radiotherapy to treat cancer
Babies, young children and elderly people are at a particularly high risk of developing oral thrush, as are people with certain underlying conditions, including diabetes, an iron deficiency or vitamin B12 deficiency, an underactive thyroid (hypothyroidism) and HIV."