What causes blisters to break out on your mouth?

Blisters on the mouth can be caused by several factors, including viral infections like herpes simplex virus, which leads to cold sores. Other causes include irritation from chapped lips, allergic reactions to food or products, or physical trauma from biting or burning the mouth. Additionally, conditions like aphthous ulcers (canker sores) can also result in painful blisters. Stress and weakened immune systems may further exacerbate the likelihood of outbreaks.