Is oral thrush contagious when kissing?

Potentially.: Thrush is an infection of the oral cavity caused by yeast (candida). Most individuals with a healthy immune system have good resistance to yeast infections, so kissing is usually safe. But there can be confounding factors. Steroids such as oral Prednisone or inhaled steroids for asthma; numerous antibiotics (oral or iv) can predispose to yeast infections. Clearly hiv/chemo patients are more prone.