Adults usually experience a fever when their body temperature rises above 100.4 °F (38 °C). This is referred to as a "low-grade fever." A high grade fever is defined as a body temperature of 103°F (39.4°C) or above. Children may have a fever without feeling hot or cold. Their body temperature may be checked with a thermometer. The type of fever you have depends on what part of the body is making the heat. If your blood moves through small capillaries, such as those in your skin, then you have a red hot sensation. The sweating also helps to lower your temperature. Without sweating, you would die before your body could cool down. You can think of the human body like a house. There are three ways to keep it warm: 1 insulation - layers of clothing worn by people who live in cold places; 2 air conditioning - machines used to produce a cooling effect; 3 heat generated by bodies functions - such as our hearts pumping out blood that heats up during exercise or digestion. A fever is caused by your body trying to fight off an infection. Your immune system triggers the production of more white blood cells and proteins which help destroy harmful bacteria and viruses. In addition, hormones released during stress changes can cause fever even when there's no detectable source of infection.