Why  fever appears and why it rises in the evening and night


Why  fever appears and why it rises in the evening and night
Do you know what fever is, why it arises and above all why it increases or rises? We reveal all you need to know about the increase in temperature in the body.

Far from what you probably think, and how many people tend to think in a regular and everyday way, did you know that fever is not negative, much less bad for your health? It is more, is part of the defense system of our own body, thus becoming a response of our body to a certain disease, condition or condition.

We tend to mistakenly think that fever is negative when the reality is quite different: far from becoming a problem, it stands out fundamentally for being an important part of the defenses of our organism. Hence, knowing why it rises or increases and especially why it appears is especially useful to bury some myths and beliefs that are not right. But let’s go in parts … what is it and what is the fever?


The fever basically consists in the temporary increase of the temperature of our organism. It is, more specifically, a set of symptoms whose main sign is that of hyperthermia (ie, the increase in temperature above the normal hypothalamic value).

However, we must differentiate it from the heat stroke since it occurs above all when there is a failure of the heat evacuation systems. However, in the case of fever, it is a reaction of our body to some external agent, when the body temperature rises to a higher level as an immune response.

Of course, for there to be the fever in an adult body temperature should be above 37.2 – 37.5 ° C (99 – 99.5 ° F), while in the case of children there will be fever from 37.2 ° C when the temperature Measure you under the arm.

Some facts to keep in mind
We must bear in mind that the normal body temperature of our body can change and vary throughout the day. For example, it tends to be higher at the beginning of the night, while physical activity, the outside temperature in the environment, certain emotions … can increase the temperature of the body without being a consequence of some type of infection.

In the case of women, for example, it is common for their temperature to vary throughout their menstrual cycle, so that during the second part of this cycle their temperature tends to rise by one degree or more.

Why does the fever rise?
It is necessary to always keep in mind that fever is an essential part of our body’s defense system against infections. That is, fever is actually a positive reaction, which means that our body is fighting for the person. Therefore, when our temperature rises to become a fever it means that our immune system is “fighting” against an infection.


High fever is usually more common in children, mainly because they have a poorly developed immune system.

While the normal body temperature oscillates between 35 and 37 ºC, above 37.2 ºC it tends to be called a low-grade fever. On the other hand, we must know that fever above 40.5 ° C can cause cellular stress, heart attack, delusions, tissue necrosis and threaten proteins of vital importance.

And why does the fever rise in the evening and in the evening?
Actually, the fact that the fever rises in the evening or at night is due to the biological rhythms of our own body. That is, it does not mean that we are more or less sick during those hours when the fever increases.

The one in charge of regulating the temperature of the organism throughout the day is the hypothalamus, a gland of the brain that helps maintain the balance of the different internal bodily functions, among which is precisely the body temperature.

And how does the hypothalamus act to regulate our body temperature? It is capable of comparing the temperature located in this gland with that of the skin, always taking the reference temperature as 37ºC. In this way, if the body temperature is higher than those 37ºC, it sets in motion different mechanisms to decrease it.

What’s more, the temperature of our body is not always the same throughout the day. For example, it tends to be lower between 2 and 4 in the morning and is much higher between 18 and 22 hours. It is for this reason that the fever increases during the afternoon and during the night: not because we are sicker, but because of the circadian rhythm of our own organism.

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