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Allergens in the nose. Scanning electron micrograph of allergens (round particles) caught in the ciliated epithelium than lines the inside of the nose. Particles like this are continuously filtered out of inhaled air by the nasal epithelium, which is carpeted by cilia and immersed in a layer of sticky mucus. Wave-like beating of the cilia pushes the mucus and foreign particles towards the throat, where they are swallowed and inactivated by stomach acid. Proteins on the surface of some particles, such as household dust and pollen, can trigger an allergic reaction in sufferers of hay fever and asthma. Magnification x4000 at 10x8 inch size. (KEYSTONE/SCIENCE PHOTO LIBRARY/E. GRAY)