Raynaud's phenomenon. The normal response to cold temperatures is to shunt blood away from the skin to keep the internal organs warm. In people with Raynaud's phenomenon, that natural response is extreme. The tiny blood vessels get severely narrowed and markedly reduce blood flow to the skin, most often in the fingers and toes. One or more digit turns white or blue, temporarily. People with Raynaud's tend to be much more sensitive to even minor drops in air temperature than other people. In addition to wearing gloves and thick socks, they need to keep their core body temperature up by wearing lots of layers of clothing.