This animation shows the immune system reacting (or overreacting) at the cellular level. It describes what happens when an allergen, like dander or pollen, enters the body. It also shows how some allergy medicines work, like anti-histamines.

The sinuses in the skull can become blocked and inflamed leading to pain and sometimes fever. The traditional surgical treatment for blocked sinuses was to use rigid instruments to enlarge the areas that drain the sinuses. A newer approach, which is shown in this animation, involves the insertion and inflation of a balloon to expand the sinus outlets. This approach is similar to balloon angioplasty used in damaged or blocked blood vessels.