When is hot weather harmful?

Our bodies are designed to maintain a temperature of about 37 degrees Celsius (°C), which is the same as about 98.5 degrees Fahrenheit (°F). If we need to cool down, our blood vessels get wider and we start to sweat.

If that makes us lose too much fluid, sodium and other electrolytes, it puts strain on our circulation – especially if we're also working hard, mentally or physically. That can lead to heat exhaustion.

Low salt levels in muscles can also cause painful heat cramps.

The skin can become irritated, too. Heat rash (prickly heat) is caused by heavy sweating. The rash can be seen as little red spots or blisters – mainly on the neck, the upper chest, and areas of the body where skin is touching skin, like the armpits and the groin.

If your body overheats, more blood flows to your skin to release some of the heat. Then your blood pressure decreases. Your brain may get less blood as a result, leading to heat exhaustion.

If the sun shines directly onto your uncovered head during hot weather, the membranes covering your brain may become irritated and the brain tissue might start to swell. This is known as sunstroke.

If the body absorbs more heat than it can get rid of, your body temperature starts to rise very quickly. Sometimes this gets out of control, leading to heatstroke. A body temperature of over 42°C (107.6°F) is already life-threatening after a short time.

Other possible health effects of heat include more injuries (for example, from falls due to dizziness), skin conditions (including sunburn and eczema), and problems during pregnancy and birth. There is already proof that more people die during and after extremely hot weather in Germany. There is also an increase in suicide attempts and aggressive behavior.

Whether dealing with individual hot days or extreme heat waves, exposure to heat can seriously affect your health.

Although the spots and blisters can be annoying, they're harmless. They normally go away again within a few days. Until then, it can help to avoid sweating if you can and keep your skin dry. You shouldn’t scratch the rash because the skin could become infected otherwise. Most lotions and creams do more harm than good because they keep the skin warm and moist. But a steroid (hydrocortisone) cream may be used if the symptoms are more severe.

The German Meteorological Office describes hot weather as “severe” if the air temperature is 29°C (84.2°F) or hotter for at least two days in a row and it hardly cools down at night. The heat is said to be “extreme” if the air temperature is 35°C (95°F) or more. But heat stress doesn’t only depend on the air temperature. Direct sunlight, high humidity and a lack of wind make it feel hotter and are harder on the body.

It is not possible to say that heat generally becomes dangerous above a specific air temperature. One reason for this is because everybody copes differently with heat. And that will also depend on how easily you are able to cool down.

Healthy adults can usually regulate their body temperature well. Hot weather is particularly dangerous for the following groups of people:

• Babies and toddlers
• Older people and those who need nursing care and live alone or in care homes
• People who rely on help, such as those with dementia
• Chronically ill people, like those with respiratory, kidney, cardiovascular or metabolic diseases (such as diabetes or obesity)
• People who take sedatives, diuretics or blood-pressure-lowering medications
• People who take antipsychotics, anticholinergics or antidepressants
• People who drink alcohol or take psychoactive drugs during hot weather
• People who work outdoors and/or people who wear protective work clothing
• People with psychological illnesses such as depression or schizophrenia
• Athletes who train outdoors or in rooms without air conditioning
• People with poor physical fitness
• People who are overweight or underweight
• People with an acute fever
• Pregnant women and their unborn children

Towns and cities are more likely to be affected by very hot weather with no cooling down at night (compared to rural areas).

There are various things you can do to stay healthy during a heat wave.

It is important to eat the right things and drink properly:

• Drink more: The best things to drink are cool – but not too cold – drinks without alcohol in them, like water, herbal or fruit tea, or juice spritzers (with not much juice and plenty of water).
• Light foods: Vegetables, salads and fruits with a lot of water in them are easier on your body than fatty foods that are hard to digest.
• Electrolytes: People who sweat a lot can best replace electrolytes such as sodium and potassium by eating foods seasoned with table salt and by drinking fluids with electrolytes in them.

The temperature in your home shouldn’t be above 26°C (79°F). To make sure it doesn’t get hotter than that, you can

• keep rooms dark during the day so the sunlight doesn’t heat them up too much,
• use a fan to help you feel cooler,
• turn off heat sources such as ovens and other electrical appliances, and
• air the rooms at night and in the morning when it's cooler outside, and keep doors and windows closed during the day. But if the rooms in your home become very humid – for example, from cooking or drying clothes – it can be a good idea to air them briefly and intensively (perhaps using a fan, too) during the day as well.

It is important to protect yourself from the heat when outdoors. You can

• adjust your daily schedule and try to do outdoor activities in the mornings or evenings,
• avoid direct sunlight and stay in the shade whenever possible,
• wear airy, light-colored clothing made from naturally cooling fabrics such as cotton or linen, and
• use lightweight bedding when sleeping – a sheet is usually enough to cover up on warm nights.

It is also important to protect your skin from UV rays by using sunscreen with a high sun protection factor. You can protect your head and eyes with a wide-brimmed hat and sunglasses.

Babies and toddlers need special protection from the sun and heat. Children under one year old shouldn’t be directly exposed to the sun at all if possible, and children who are older than that shouldn’t spend too much time in direct sunlight. Frequent sunburn, especially in early childhood, greatly increases the risk of skin cancer in later life. You should be particularly careful in the midday sun between 11am and 4pm because that's when UV radiation is strongest.

Older people and those in need of nursing care often need extra support in very hot weather – like making sure they drink enough fluids or helping them to buy their groceries. Family, friends, caregivers and neighbors can provide valuable assistance here.

To be better prepared for hot summer days, you can also talk to your doctor beforehand about whether you might have to adjust any medication such as diuretics or blood-pressure-lowering medications.