An itchy and swollen mouth may have angioneurotic edema, which is usually caused by allergies. Usually it is caused by eating allergic foods or taking allergic medications. It is usually treated with anti-allergy medications, such as paracetamol or loratadine, and the angioneurotic edema usually heals on its own. Itchy and swollen mouths, and possibly clusters of small blisters, are caused by the herpes virus, which can easily appear if the body is immunocompromised and recur. It is usually treated with antiviral medications, commonly acyclovir or ribavirin, and can also be treated with topical acyclovir ointment, which can promote rapid regression of the herpes.