Small blisters on the side of the mouth, medically known as blisters, can be caused by herpes simplex, xerostomia, allergies and other causes. 1. Herpes simplex: blisters on the side of the mouth are mostly seen in patients with herpes simplex. Perioral herpes simplex is a viral skin disease caused by patients infected with herpes simplex virus type 1. Herpes simplex is usually found in the corners of the mouth area, the lips, and the skin and mucosal migratory tissue portions around the nostrils. For patients with herpes simplex, antiviral medications such as acyclovir and valacyclovir can be used under medical supervision. 2. Keratitis: the lack of B vitamins, may also lead to small blisters on the side of the mouth, oral vitamin B2 or vitamin B complex and other treatments, daily attention to diet and nutritional balance. 3. Allergy: can be caused by eating certain allergenic food, such as mango, pineapple, or allergic to lipstick, resulting in local allergic reactions, blisters, itching symptoms. You need to wash the local area immediately, find the allergen as soon as possible, and avoid re-exposure. Severe symptoms can be treated with oral anti-allergy drugs such as loratadine. When you have small blisters on the side of your mouth, you should pay attention to your diet to avoid eating spicy and stimulating foods, and you should arrange your work and rest time reasonably, don’t stay up all night. Strengthen exercise, enhance the body’s immunity. It is recommended that patients should go to the dermatology department in time, after clarifying the cause of the medication under the guidance of the doctor, do not blindly use their own medication, so as not to aggravate the symptoms, or cause unnecessary damage to the body.