Trachea covered in allergens. Coloured Scanning Electron Micrograph (SEM) of the surface of the trachea (windpipe) with breathed in pollen and dust. These airborne particles may cause asthma or hay fever (allergic rhinitis). Pollen grains are coloured pink. The surface of the trachea is made up of cells with hair-like cilia (yellow). Together with mucus, these cilia serve to trap airborne particles and by beating upwards in a wave-like motion they remove foreign matter from the air tubes and lungs. In asthmatic or allergic patients, such particles may lead to a hyper- sensitive reaction causing breathing difficulties. Magnification: x1130 at 5x7cm size. x4,000 at 8x10 inch size.