Blisters inside the mouth that are relatively small and densely distributed in patches are indicative of herpes stomatitis, caused by infection with the herpes simplex virus at a time when the body is immunocompromised. Large, dense, pinhead-sized blisters appear on the mucous membrane of the mouth and cheeks, leaving a red, swollen, congested mucosal surface after the blisters break down. If blood blisters or blisters appear in a certain part of the mouth, it is mostly due to the consumption of spicy and irritating foods, overly hot foods and hard foods, which cause irritation and trauma to the mucous membrane, resulting in blisters or blood blisters on the mucous membrane. The presence of dental caries or sharp tooth tips, root stumps, crown stumps, bad restorations, etc., which can often scratch or bite the mucous membrane in the wound, will also cause the corresponding parts of the mucous membrane to appear blisters and blisters.