Hay fever sufferers can now see the face of their invisible enemy - thanks to these Scanning Electron Microscope images of pollen grains. A Swiss scientists named Martin Oeggerli, who uses the name Micronaut for his art, uses a Scanning Electron Microscope in his cellar to capture images of pollen grains. This picture shows a grain of willow pollen wedged between flower petals. Birch pollen, one of the most common causes of hay fever in Britain. Birch trees release their pollen between March and May, and hay fever sufferers are likely to experience the worst symptoms during April. Pollen from a forget-me-not. This flower has one of the smallest known grains of pollen; just five one-thousandths of a millimetre in diameter. Up to half of the British population suffer from hay fever, which is caused by the immune system reacting to the pollen. Cells inside the nose and eyes release histamine and other chemicals when they come in contact with pollen, causing red eyes and a blocked nose.