An allergy is a general term used to describe hypersensitivity to a substance that it identifies as harmful, even though it may be perfectly safe. The trigger that causes the allergic response is called an allergen. Many people experience an itchiness in the mouth when they're having an allergic reaction to food. Hay fever, another allergic reaction, can cause the same symptom. Occasionally an itchy mouth can be caused by cross-reactivity between two substances.
Hay Fever
Hay fever, also called allergic rhinitis, is a reaction to airborne particles, such as pollen, mold spores, dust mites or animal dander. Hay fever causes cold-like symptoms, such as watery eyes, sneezing, coughing, post-nasal drip, stuffy nose and headache, according to PubMed Health. An itchiness in the back of the throat or the mouth is another common symptom. There is no cure for hay fever, aside from avoiding the allergens. Most are difficult to completely eliminate, though, so your doctor may recommend a daily antihistamine.
Food Allergy
A food allergy can cause itching anywhere on your body. Because your mouth is the first part of your body to come into contact with the food, you may develop itching in your mouth and throat. The most common foods that cause an allergic reaction include wheat, soy, peanuts, fish, tree nuts, milk and eggs, according to the Mayo Clinic website. An allergic reaction to food causes histamine levels to rise in soft tissue and leads to irritation and inflammation throughout the digestive system.
Oral Allergy Syndrome
Sometimes a cross-reactivity can cause a condition called oral-allergy syndrome. If you're allergic to certain pollens, your mouth may begin to itch if you eat certain raw fruits, vegetables or nuts that your body mistakes for the primary allergen. For example, if you're allergic to birch pollen, eating peppers, hazelnuts, almonds, walnuts, apples, pears, apricots, plums, kiwi, carrots or potatoes could cause your mouth to itch, according to the Children's Hospital of Philadelphia. Symptoms of oral allergy syndrome may be prevented by cooking the food before you consume it.
Consideration
Mouth itching that leads to swelling in the lips, tongue, mouth or throat may be a sign of a severe allergic reaction. Call 9-1-1 if you develop swelling in your mouth. While anaphylaxis is rare, the condition can lead to death if it is not treated properly. The most common treatment for a severe allergic reaction is an injection of epinephrine.
