Technically, a fever is any temperature above your normal temperature; most adults' normal temperature is 98.6° Fahrenheit. A low-grade fever for most adults would be slightly elevated, between around 98.7° F and 100.4° F, for a period of 24 hours. A high-grade fever is usually in the 103-104° F range and is cause to seek medical attention.

For infants and toddlers, the threshold is slightly lower. You should seek medical attention for a child under 3 months who has a rectal temperature of 100.4° F or higher. For children 3 to 6 months, seek medical attention if they’re especially irritable, lethargic or uncomfortable with a rectal temperature of 102° F, or have a rectal temperature above 102° F. For children 6 to 24 months, seek medical attention for a temperature of 102° F or higher that lasts longer than a day with no other symptoms; if they have other symptoms, you can seek medical attention sooner.

No. For example, people in Alaska don't get more colds than people anywhere else. We do have more colds in winter than in summer, but not because of the cold (see more on why below). Cold weather conditions play no role except as mentioned below about absolute humidity levels in the winter. One of the expert scientists (Bill Nye) said that you can not catch a cold from being cold; you catch a cold from germs and being cold has nothing to do with it. Plenty of tests have been conducted proving this.

The old belief that freezing temperatures cause illness started before people knew about germs; however, it continues to be passed along to others as a legend today and is not an evidence based finding from studies - just based on anecdotes and incorrect associations.

It has been scientifically studied with double blind test groups and there was no difference found in the rate of infection with common cold viruses when the study groups were exposed to cold temperatures or heat via different methods. The results of those studies were peer reviewed. "No" has become the current most accepted answer to the question by scientists and medical professionals.

Then why do we get more colds and flu in winter and cold weather?

It had been long held that this was most probably due to school children returning to schools and people being in closer proximity indoors in winter where they could pass all their germs around more easily. One of the most commonly cited studies used as a basis for this hypothesis was the "Seattle Virus Watch", done by John Fox, Carrie Hall, and friends.

Another hypothesized explanation had been that our Vitamin D production is lower in winter due to less exposure of our skin to sunlight, and since Vitamin D improves the immune system's ability to fight off infections, our defenses are made weaker in winter with Vitamin D deficiency. Another commonly held belief was that in drier air our mucous tissues dry out and can crack, making the viruses more easily introduced to the body. Some combination of all these factors may be at play.

However, the most recent studies have all seemed to point more to the different absolute humidity levels in winter compared to those in summer. Cold and flu viruses like it dry. See the related question below, "Why does the flu have a season?" for more details about these recent findings.

Check out the discussion section for comments, anecdotes, and discussion.

It is often believed that colds and flu and other infectious diseases can be caused by cold weather, changes in temperatures, being wet outside, or having wet hair, etc. None of this is correct information.

People also often say that being cold affects your immune system so you are more susceptible to infections. This is also not correct. When this is discussed, it doesn't just mean feeling chilly or even getting "goosebumps" or shivering. Hypothermia can have negative effects on your entire body including the immune system, but just being cold is not hypothermia. When medical studies use that term, it is used to refer to a specific measurement of core body temperature.

Hypothermia is not the same as being cold, it is a specific medical diagnosis and:

• It is defined as a core body temperature that is at or below 95 F (35 C).
• Needs to be treated if body temperature goes below 95 F (35 C).
• Becomes life threatening below body temperatures of 90 F (32.2 C).
• Affects motor coordination through impact to the nervous system at 95 F.
• When the body temperature drops that low, at the start of a hypothermic condition, symptoms can include intense uncontrollable shaking and shivering, then if your body continues to get colder, the shivering stops when the core temperature gets between 90 F and 86 F.
• It causes heart rate, respiratory rate, and blood pressure to rise during the first stages of hypothermia as your body tries to increase metabolism and warm itself, but these vital signs fall once the temperature gets 90°F (32.2°C).
• Creates coma at below 86 F.
• Heart rate becomes very irregular below 82 F and death can soon follow.

The reason the disease is called a "cold" does come from the myth and misunderstandings from back when it was thought that upper respiratory viral infections were caused by cold since most often occurred in cold times of the year and when they had no clue about disease-producing microbes. We know that is incorrect now, but the popular name of the "common cold" has not changed to its more proper name: a Rhinovirus infection.

The average human body temperature is 98.6º F or 37º C, but it can vary somewhat. Older people average a bit less. These values can also vary with time of day.

This means that illness may be present, especially in older adults, even when the temperature appears to be within the normal range. It is important for some to establish baseline values on an individual basis, since significant variations from the norm can occur in some individuals.
13oC
Average 98.6deg F, 37deg C

Average body temperature is 98.6 F