Your feet can show signs of illness well in advance. Medical conditions such as diabetes, arthritis and a lot of other disorders that are associated with the circulatory system and nerves show their initial effects on your feet.
You can tell if the person is unwell only by touching their feet. When unwell, your feet turn cold due to poor circulation. The colour of your toenail can also tell you about your upset stomach, weak liver and a lot of other stomach related issues. So, the next time you get cold feet (literally), visit a doctor and get yourself examined.