Countries in Western and Central Europe - including Spain, France and the United Kingdom - have issued red alerts because a heat wave is expected to intensify in the coming days with temperatures that will exceed 40 °C.

The immediate cause of this increase in temperatures is a “heat dome”: a mass of warm air moving north from the Sahara is “stuck” over Europe, trapping hot air inside.

This mass is fed by a powerful high pressure system known as the “African anticyclone.”

Scientists stress, however, that there is no doubt that the recurrence of heat waves is an indicator of human-caused climate change, largely the result of the burning of coal, oil and gas.

The heat wave is expected to continue although temperatures will drop somewhat starting Thursday.

But what effect can extreme heat have on our body? We explain what happens to your body when it is exposed to high temperatures, and how to take care of yourself to reduce its impact.

What does extreme heat do to our body?

As the body warms, the blood vessels dilate, opening. This causes us to have lower blood pressure and the heart to work harder to push blood throughout the body.

This can cause mild symptoms, such as an itchy rash or swollen feet.

At the same time, we will start to sweat, and this leads to the loss of fluid and salt and, crucially, changes the balance between them in the body.

This, combined with low blood pressure, can cause heat stroke or heatstroke. Symptoms include:

If blood pressure drops too quickly, the risk of heart attacks increases.

Why does our body react this way?

Our body strives to maintain an internal temperature of approximately 37.5°C, whether we are in the middle of a snowstorm or a heat wave.

It is the temperature at which our body is accustomed to working.

But as the weather gets warmer, the body has to work hard to keep its internal temperature down.

That is why the blood vessels closest to the skin dilate, to expel that heat and you begin to sweat.

As sweat evaporates, heat loss is drastic and the skin cools down.

How can I stay safe from the heat?

The health authorities give some advice in this regard:

What foods should we eat or avoid during heat waves?

The most advisable thing is to follow a varied and balanced diet, with a Mediterranean pattern (which includes seasonal products, mainly of plant origin, such as fruits, vegetables, legumes, cereals and olive oil), as explained by Carmen González Vázquez, professor in the Degree of Human Nutrition and Dietetics at the International University of La Rioja, Spain, in an article in The Conversation.

It is preferable to eat light and fresh meals throughout the day, avoiding very abundant and high-fat meals, as well as avoiding excess consumption of proteins from large animals, such as beef or lamb.

It is also important to choose foods that contain more water, and, if possible, opt for foods that are eaten raw or that require little cooking.

How can I keep my house cooler?

How can you sleep well?

Use thin sheets, and if you are one of the people who cannot sleep without socks, put them to cool in the refrigerator before putting them on and follow your usual routine before going to bed, experts recommend.

If the heat is very intense even at night, use a fan and open the windows to create drafts.

What should I do if I see someone suffering from heat stroke or heatstroke?

If the person can cool down and return to a lower temperature within half an hour, then heat stroke is not serious.

Health authorities advise:

If after having done all this you do not recover within 30 minutes, what follows is sunstroke.

This is a medical emergency and you should call emergency services.

People who suffer from sunstroke or heat stroke stop sweating even if they are too hot. Their temperature may exceed 40°C and they may have seizures or lose consciousness.

Who is most at risk?

Old age or some chronic ailments, such as heart disease, can make people less able to cope with the stress that heat puts on the body.

Diabetes can cause the body to lose water more quickly, and some complications in this disease can alter blood vessels and the ability to sweat.

Children and those who are less mobile may also be more vulnerable.

Brain diseases, such as dementia, can also cause some people to be unaware of the heat or unable to do anything about it.

Homeless people will also be more exposed to the sun.

Are there medications that increase the risk?

Diuretics, sometimes called “water pills,” increase the amount of fluid expelled from the body. They are widely used, even for heart failure. With high temperatures, the dangers of dehydration and imbalances in some minerals that are key to our body increase.

Antihypertensives, which lower blood pressure, have an effect that, combined with the dilation of blood vessels due to heat, can cause dangerous drops in blood pressure.

Some epilepsy and Parkinson's medications can block sweating and make it harder for the body to cool down.

Other medications such as lithium and statins can become more concentrated and problematic in the blood if there is excessive fluid loss.

Can heat kill?

Yes, in cases of heat stroke, which occur when the body has sudden increases in temperature and cannot be lowered, according to the Mayo Clinic in the USA.

Most deaths usually occur from heart attacks and strokes caused in turn by the body's effort to try to keep body temperature stable.

The evidence suggests that many of the deaths occur with high temperatures in spring or early summer, rather than during the “summer peak.”

This may be because, at first, we are not yet acclimatized and then, as the summer progresses, we adapt our day-to-day behavior, habits and clothing and get used to dealing with the heat.

The evidence from previous heat waves is that the increase in deaths occurs very quickly, within the first 24 hours of the heat wave.