Oral thrush is not contagious, but it can be passed on in circumstances where the body's immune system is compromised, according to WebMD. Conditions that can compromise the immune system include diabetes, dry mouth, pregnancy, not taking care of one's teeth, and taking antibiotics or inhaled corticosteroid medicines.
Because of this possibility, WebMD suggests adults refrain from kissing while thrush symptoms are present. Caution should also be taken with infants who have undeveloped immune systems, older adults who have weakened immune systems, and people with human immunodeficiency virus (HIV) who are likely to get thrush. Patient.co.uk explains that thrush is caused by the Candida yeast, which occurs naturally in the body.