Like a toppling line of dominoes, one allergic reaction can lead to another. If you've ever suffered hay fever or other allergies, you know that the sinuses are the first to go. Your nose runs and you feel congested. This is due to the body's reaction to histamines, substances that are produced when allergens react with the antibodies that your system produces to combat them. If you could see inside your head, you'd see that the mucous membranes in your sinuses are swollen. In some people, especially small children, this can produce ear problems as well. The middle ear drains through the eustachian (YOU-STAY-SHE-UN) tube into the throat. This equalizes the pressure in the ear. Swollen sinus membranes can block the eustachian tube, causing pressure to build in the ear. Children are particularly susceptible because their eustachian tube is smaller and more easily closed. An ear, nose, and throat specialist can relieve the ear pressure and offer professional advice on how to deal with your allergies, as well.