Red spots in the mouth can be caused by canker sores, allergic reactions, vitamin deficiencies, oral trauma, stress or a systemic disease, according to MedicineNet.com. Patients who observe red spots or sores in their mouth should visit a doctor if the spots do not disappear within a few days.
Canker sores are the most common causes of red spots in the mouth. They are ulcerated sores in the mouth caused by exposure to irritating foods, stress or other types of trauma, according to WebMD. Most canker sores disappear on their own.
Vitamin deficiencies can also cause red spots to appear in the mouth. The most likely culprits include deficiencies in B vitamins, zinc and iron.
When a person eats a food to which he or she is allergic, red spots might appear on the tongue or roof of the mouth. Allergies can also create redness or swelling on the lips or around the mouth.
Stress is also a common reason for the development of red spots in the mouth. Experts do not fully understand the cause, but stress can present itself in physical symptoms as well as psychological ones.
In some cases, red spots are due to oral trauma. If the patient bites the inside of his or her cheek, for example, a red area might appear. The same is true if the surface of a tooth has become rough or if the patient wears a mouth appliance, such as braces.