Fever is when a human’s body temperature goes above the normal range of 36–37° Centigrade (98–100° Fahrenheit). It is a common medical sign.

Symptoms:

When somebody has a fever, signs and symptoms are linked to what is known as sickness behavior, and may include:

• feeling cold when nobody else does
• shivering
• lack of appetite
• dehydration — preventable if the person drinks plenty of fluids
• depression
• hyperalgesia, or increased sensitivity to pain
• lethargy
• problems concentrating
• sleepiness
• sweating

If the fever is high, there may also be extreme irritability, confusion, delirium, and seizures.

Types:

Fevers can be classified according to how long they last, whether or not they come and go, and how high they are.

Severity:

A fever can be:

• low grade, from 100.5–102.1°F or 38.1–39°C
• moderate, from 102.2–104.0°F or 39.1–40°C
• high, from 104.1–106.0°F to or 40.1-41.1°C
• hyperpyrexia, above 106.0°F or 41.1°C

The height of the temperature may help indicate what type of problem is causing it.

Length of time:

A fever can be;

• acute if it lasts less than 7 days
• sub-acute, if it lasts up to 14 days
• chronic or persistent, if it persists for over 14 days

Fevers that exist for days or weeks with no explanation are called fevers of undetermined origin (FUO).