Catarrh is a medical condition that is characterized by inflammation of the mucous membranes in the nose and throat. It is often caused by an infection, but can also be triggered by allergens such as dust, pollen, or pet dander. Rheum, which is a five-letter word, is a type of mucus that is produced by the body in response to inflammation. Allergens, which is a nine-letter word, are substances that can cause an allergic reaction in some people.