Sub-zero temperature refers to temperatures below zero degrees, either in Celsius or Fahrenheit scales. It is a convenient way to say that the temperature is going to be very cold, and it is usually used to refer to negative temperatures. In the United States, sub-zero means below 0°F. In products with an electronic control panel, the ideal food storage temperatures for a refrigerator are set to 38°F (3°C) and for a freezer are set to 0°F (-18°C) . Sub-zero temperatures can be harmful to humans and animals, and can cause hypothermia, frostbite, and other cold-related illnesses.