Oral thrush: Causes, Symptoms, Treatment | Oral thrush contagious Straight from your Specialist Doctor Oral thrush is a yeast infection which develops, on the inside of the cheeks, on the tongue, on the tonsils and the gum pads, so which is generally known as oropharyngeal candidiasis or commonly called as candidiasis. The main cause of the oral thrush is because of candida albicans fungus which causes oral thrush and its management. The dentist may advise the patient to discontinuing the curren