You've probably heard that the typical body temperature for a human is 98.6 degrees Fahrenheit (37 degrees Celsius). That's actually an average -- body temperatures fluctuate throughout the day and can depend upon a person's age or activity level. But it's a good rule of thumb -- if your temperature drops lower or rises higher than the average you may begin to experience health problems.
A fever is a good example. Fever is usually a defense mechanism -- it's the body's response to protect against infection. Most bacteria that cause infection thrive at the body's typical temperature. Raising the temperature inhibits the infection. A part of your brain called the hypothalamus is in charge of maintaining body temperature. Think of it as controlling your internal thermostat -- if you get an infection, the hypothalamus cranks up the temperature dial a couple of notches to slow the infection down [source: The Merck Manuals].
Another example is hyperthermia. Hyperthermia is an elevated body temperature, but it's not like a fever. With a fever, the hypothalamus has reset the body's internal thermostat. Hyperthermia is a symptom that sets in when the body isn't able to maintain temperature properly -- it literally overheats. Hyperthermia can be serious. If the body's temperature rises too high, your organs can suffer damage.
Generally, hyperthermia isn't a disease. It's a side effect of another problem, just like itching is a side effect of an allergic reaction to poison ivy. There is a condition called malignant hyperthermia that's an inheritable disease, but it's not the same thing as the symptom hyperthermia.
Hyperthermia isn't always bad, either. Doctors are experimenting with inducing hyperthermia as part of an overall approach to treating cancer. But elevating the body's temperature under medical supervision and experiencing hyperthermia on your own are two different situations. Hyperthermia can be a warning sign that you're about to be in some serious trouble.
Let's look at what causes hyperthermia.