The average normal body temperature is 98.6°F (37°C) when taken orally (by mouth). It might be lower in the morning and then get higher as the day warms up. A mild elevation of body temperature of 100°F (37.8°C) might be caused by too much clothing, a hot bath, or hot weather.

Fever is usually a sign of illness. You may have a mild fever of less than 101°F (38.3°C) with a sunburn. Home treatment is usually all that is needed to treat a mild fever. If your fever increases or continues for longer than 1 day, or if other symptoms develop, an evaluation by your health professional may be needed.

A fever may be a sign of a heat-related illness. Heat exhaustion occurs when your body cannot sweat enough to cool you off. It can happen when you are working or exercising in hot weather or getting sunburned. Given the right conditions, heat-related illnesses can also develop in hot indoor environments.