You may be wondering what does asthma have to do with cavities. When people aren’t easily able to draw in their breath, most people compensate by breathing through their mouths. This causes your mouth to dry out. Insufficient saliva leaves you more vulnerable to decay-causing bacteria because saliva helps to protect and clean your teeth. Moreover, asthma and allergy medications themselves can cause even more dryness on top of mouth breathing. In short, it’s not a good combination.