Temperature during flu – danger or benefit?

Doctors often say that patients exaggerate the danger of high temperatures. But 39–40 °C on the thermometer is a cause for concern, especially if a child is sick. We figure out when a temperature during flu in adults and children is dangerous and when it is not, in which cases it is necessary to bring down the fever and how to do it correctly.

Why does the temperature rise with the flu?

An increase in temperature is a protective reaction that occurs in response to the penetration of a pathogen into the body.

Maintaining a constant body temperature is a complex process involving the immune, endocrine and nervous systems. The thermoregulation center is located in the hypothalamus, a small part of the brain.

When the flu virus enters the body and begins to multiply inside the cells of the respiratory tract, the immune system begins to produce inflammatory cytokines (interferons, interleukins, etc.). They help the body fight viruses, but at the same time stimulate the synthesis of prostaglandins, which “switch” the thermoregulation center. The body begins to perceive normal temperature as lower, and the “set point” shifts. The thermoregulation center activates heat production and reduces heat loss, so the body temperature rises.

At high temperatures, the processes that help the body fight infection are more intense:

• the production of antibodies and interferons increases;
• the activity of neutrophils, blood cells that absorb pathogenic microbes, increases;
• the liver’s ability to detoxify is enhanced;
• stimulates kidney function;
• the synthesis of proteins that participate in the body’s defense increases;
• The content of iron, copper and zinc in the blood decreases, which slows down the reproduction of pathogenic microbes.

The optimal temperature for these processes is 39 °C. ¹

It turns out that fever during flu helps the body fight the infection faster. But at the same time, high temperature has a number of negative effects:

• the load on the cardiovascular system increases – with each extra degree the heart rate increases by 10-15 per minute, blood pressure may increase;
• due to increased sweating and rapid breathing, the patient loses a lot of fluid;
• with prolonged and strong increase in temperature the kidneys are damaged;
• absorption in the gastrointestinal tract is disrupted, patients lose their appetite;
• metabolic disorders occur – increased blood sugar levels, loss of protein;
• Children and patients with nervous system diseases may experience seizures.

What temperature usually occurs with flu

While other acute respiratory viral infections may occur with normal body temperature, flu is almost always accompanied by fever. As a rule, this is the first sign of the disease.

The temperature with flu usually rises suddenly and sharply. Already in the first hours of the disease it reaches 38-40 °C. ² High temperature is accompanied by chills and signs of intoxication : headache , pain when moving the eyes, muscle and joint aches , loss of appetite, weakness.

In children in the first months of life, flu often occurs in an atypical form: the symptoms of the disease are weakly expressed, the temperature rises slightly. But such well-being is deceptive. It is in young children that life-threatening complications most often develop with flu. ³

How long does the temperature last with flu?

With uncomplicated flu, the temperature does not last longer than 5-6 days. Already on the third day of illness, the fever subsides, and the symptoms of intoxication also become less pronounced. ³

If the high temperature lasts longer than six days, this most often indicates the development of complications or the addition of a bacterial infection. In this case, you should immediately call a doctor.

Temperature fluctuations with flu

After the first symptoms of the disease appear, the fever usually lasts up to five days. At the same time, the temperature can decrease to subfebrile values when taking antipyretic drugs. But after a few hours it rises again, as the virus remains and progresses in the body.

With flu, immunity is suppressed. There is a risk of opportunistic flora multiplying and developing a bacterial infection in the form of bronchitis, pneumonia, and inflammation of the nasal sinuses. In this case, the temperature may rise again even after five days from the moment of illness.

Such phenomena are often observed, for example, when a person has not fully recovered and on the first day went to work or school without a fever. If a secondary infection joins in, the thermometer will again show elevated values in 1–2 days.

When to bring down the temperature

All patients tolerate fever differently: some feel normal at 39 °C, others are ready to take antipyretics at 37.5 °C.

Doctors believe that a short-term rise in temperature by 3 °C (i.e. up to 39.5 °C) is not dangerous for an adult without concomitant diseases. If the patient can tolerate the fever, it is better not to take the medicine so as not to interfere with the body’s ability to cope with the infection on its own. But a further increase in fever can be dangerous. A temperature above 42.2 °C is considered lethal. ¹

It is important to pay attention not only to the thermometer readings, but also to the individual characteristics of the patient’s body: age, presence of concomitant diseases, severity of the flu. There are categories of patients who must have their temperature brought down, even if it is far from critical values. These include:

• young children, especially those with a history of seizures associated with fever;
• patients with concomitant diseases of the cardiovascular and nervous systems;
• patients with a severe general condition (severe weakness, headache, etc.).

When does a fever become dangerous?

In itself, a temperature increase to 39 °C does not cause much harm if a person is generally healthy. But in the presence of organic lesions of the central nervous system, especially in small children, negative phenomena are possible, such as convulsions, deterioration of heart function.

Elevated temperature accelerates metabolic processes in tissues, including the brain. Cells require more oxygen, but with a viral infection, vessels cannot transport it fully. Hypoxia occurs, which can lead to headaches and impaired consciousness.

In pregnant women, a high fever due to flu for several days can lead to miscarriage or birth defects in the fetus.

Why does the temperature rise in the evening during flu?

The body’s defenses weaken at night, so the malaise often intensifies in the evening. The body, according to biorhythms, adjusts to rest and sleep and switches off the resource state. Even if you feel normal during the day and have a feeling of complete recovery, closer to night you can feel weakness, body aches and see higher readings on the thermometer.

How to reduce fever during flu

There are two ways to bring down a fever: take an antipyretic or use non-drug (physical) methods. Remember that reducing the temperature is not an end in itself when treating flu. This measure is used only to improve the patient’s well-being and avoid life-threatening consequences.

Antipyretic drugs

To reduce fever in adults and children, one of two drugs is most often prescribed: paracetamol or ibuprofen, or a combination of both.

Paracetamol belongs to the group of non-narcotic analgesics. It blocks the mechanism of occurrence of fever and pain in the central nervous system. The maximum daily dose of paracetamol for adults is 4 g per day, for children – 60 mg/kg per day. ⁴

Ibuprofen is a non-steroidal anti-inflammatory drug. It has not only antipyretic and analgesic effects, but also anti-inflammatory effects. Ibuprofen is safer than other NSAIDs: it causes gastrointestinal complications much less often. ⁵ The maximum daily dose for adults is 1.2 g, for children – 800 mg.

A clinical study published in 2020 showed that the duration of the period of fever in patients is significantly reduced by taking enisamium iodide ⁶ , the active ingredient of Nobazit® Forte ⁸ . A statistically significant difference in the normalization of body temperature was detected already on the third day of therapy. ⁶ The number of patients whose body temperature reached normal values in the group taking enisamium iodide was more than three times higher than the number of patients in the control group. ⁶ In 2021, the renowned scientific journal Therapeutic Archives published the pharmacological properties of the enisamium iodide molecule. ⁷ It was possible to establish an anti-inflammatory effect comparable to that of ibuprofen. ⁷ The additional anti-inflammatory activity of Nobazit® Forte is becoming a promising tool in the fight against the excessive use of symptomatic therapy drugs.

Non-drug remedies

These methods have a less powerful and long-lasting effect than antipyretic drugs, but often help improve well-being. Of the non-drug methods for reducing temperature, doctors recommend the following: ¹

• Cold compresses. They are applied to the forehead and areas where large vessels are located: neck, wrists, shins. A regular damp cotton towel will do. As it dries, it should be moistened with cold water.
• Wet wraps and rubdowns. Evaporation of water from the skin helps to reduce the temperature.

It is important to follow the general rules of patient care. They will help improve your well-being and speed up your recovery:

• bed rest;
• drinking plenty of fluids (necessary to compensate for fluid loss through sweating);
• regular ventilation of the room;
• change bed linen and clothes if you sweat heavily.

The patient should not be wrapped up, as this will reduce heat transfer.

What to do if the temperature does not go down

If antipyretic drugs or folk methods help to bring down the fever at least a little, that is enough. Lowering the temperature even by 1 °C (for example, from 40 °C to 39 °C) will already significantly improve the condition.

But if, despite all the measures taken, the patient’s temperature remains at 40 °C or higher, call an ambulance. The doctor will inject a lytic mixture that will help bring down the fever.

Briefly about the main thing

• Fever during flu is the body’s protective reaction to the penetration of the virus. At elevated temperatures, the immune system fights the infection more actively.
• Too high a temperature can be dangerous – it puts stress on the cardiovascular system and causes changes in organs and tissues.
• If the patient is in a risk group or does not tolerate heat well, a temperature above 39.5 °C should be brought down.
• To reduce the temperature, medications based on paracetamol or ibuprofen are used.
• Cold compresses and rubdowns, and drinking plenty of fluids will help bring down the fever for a short time.