As sweltering heat sweeps across much of the Northern Hemisphere this week, officials and public health experts have issued heat warnings to keep people safe.
China, India, the Middle East, southern Europe and parts of the United States are all set to likely set new record highs.

What are the health risks?

Heat affects health in many ways.

Heat exhaustion, which can include dizziness, headache, shaking, and thirst, can affect anyone, and is usually not serious, provided the person cools down within 30 minutes.

The most severe form is heatstroke, when the body temperature rises above 40.6 °C (105 °F). This is a medical emergency and can lead to long-term organ damage and death. Symptoms include rapid breathing, confusion or seizures, and nausea.

The risk of humidity is also expected to increase in the coming years as temperatures continue to rise due to climate change. Hot air can hold more moisture. And more moisture in the air makes it harder for people to sweat to cool down.

Who is at risk?

Some people are more vulnerable, including young children and older people, as well as people who need to stay active or who are at higher risk, such as homeless people.

Existing conditions such as respiratory and cardiovascular diseases, as well as diabetes, can also increase the risk – and may be exacerbated by heat.

Many countries do not identify heat as a specific cause of death, meaning we do not have data to assess this risk across communities.

However, a study published in 2021 in The Lancet estimated that about half a million deaths each year are caused by extreme heat – a conservative calculation that lacks data from many low-income countries.

Scientists said many in Europe fear a repeat of the summer of 2022, during which heat waves killed an estimated 61,000 people.

The risk will continue to increase in the coming decades as global temperatures rise further due to climate change.

Less obvious risks

In addition to testing the body’s internal temperature, excessive heat can also pose a number of other secondary hazards.

Warmer temperatures promote the growth of bacteria and algae. So heat waves can increase the risk of water being contaminated with diseases such as cholera or water bodies being clogged with toxic algae.

The heat can also damage crops, raising concerns about food security.

According to the World Health Organization (WHO), experts estimate that global mortality will increase by 250,000 per year by 2030 as a result of four climate-related health risks: heat stress, undernutrition associated with food insecurity, malaria, and diarrhoea.

Wildfires caused by dead trees or brush can produce dangerous levels of air pollution, which can cause lung inflammation and tissue damage.

Studies have also shown that exposure to extreme heat, as well as wildfire smoke, can also increase the risk of low-birth-weight babies and preterm birth.

Heat stress can also worsen mental health. Rising temperatures at night can disrupt people’s sleep habits, which can have a negative impact on mental health.

Importance of time

Experts say that most deaths occur in early summer, when people’s bodies do not have a chance to acclimatize to the weather.

Location also matters; people are at greater risk in places where they are not accustomed to such heat, including parts of Europe.

As working outside becomes dangerous amid high temperatures, some countries and communities have closed schools or reduced daytime working hours for businesses.

what can you do

Public health agencies from India to the United States have issued advice on keeping cool, including avoiding exertion as much as possible and drinking plenty of water.

Authorities often aim to help by setting up cooling centers, distributing extra water or providing free access to air-conditioned public transport.

Scientists say that workers should also consider taking more breaks and changing their clothes.

He said it was important to test vulnerable people, including the elderly and isolated people.

Heatstroke is a medical emergency and requires immediate professional attention.