The image shows the 'heat signature' left behind of the hand of a person experiencing symptoms of Raynaud's (on right) against that of a person who is unaffected (on left). This image shows the heat pattern left behind once the hands are lifted from the surface. Raynaud's phenomenon (also referred to as Raynaud's syndrome or Raynaud's disease) affects the bodily extremities, most commonly the hands and feet. On exposure to cold or stress, the blood vessels at the extremities constrict or narrow, restricting the flow of blood; this is called vasoconstriction. This condition has been visualized using thermal infrared which allows us to see thermal energy or radiation more commonly referred to as heat. This image shows handprints from both hands after exposure to cold water. The different colors in the images represent different levels of thermal energy being emitted from the skin's surface. In this image the yellow and orange colors show a high level of thermal energy and the blue a low level.