The signs of heat stress you need to know this summer.

Hot weather can take a serious toll on our health.

Severe and extreme heatwaves in Australia have caused more deaths than any other natural disaster in the last 200 years, the Australian Bureau of Meteorology website says.

For instance, the official death toll of the 2009 Victorian Black Saturday bushfires was 173, but 374 people died from heat-related causes during the heatwave that preceded it. (And it’s worse in other parts of the world, in Europe in 2003, 70,000 people died in a heatwave.)

It’s not just days where temperatures are above the high 30s that pose a significant health risk. Heat-related illness can also be an issue at much lower temperatures, said Associate Professor Adrian Barnett, from QUT.

“Focusing on the extreme heatwave days… does give the public the impression that the other hot, but not intensely hot, days are safe and they are not,” Dr Barnett said.

“Thirty degrees days can also be very, very dangerous and they occur far more often and they normally end up presenting the bigger problem.”

But heatwaves do increase the chances of things going wrong and that can lead to “a catastrophic failure which can really push things over the edge”, he said.

“The ambulance drivers not being able to work because it’s too hot or the hospitals getting so packed. That is especially true when you have a long power cut combined with heat because air conditioning is a great way to reduce your risk of [heat-related illness],” he said.

Who’s at risk?

Extreme heat can affect any one of us, especially if we’re spending outdoors in the heat of the day.

Those most at risk include older people, young children and those with chronic health conditions, in particular those with cardiovascular disease. The thing is, there are many people who are unaware they’re at risk of cardiovascular disease.

“So people who may not even realise they are walking around with a cardiovascular problem and a day like today is a perfect day for that problem to flare into something that requires them to call an ambulance or can even kill them.”

Another group hit hard by hot weather are pregnant women.

“Lots of studies around the world now show higher temperatures are strongly associated with an increased risk for pre-term births,” Dr Barnett said.

Other people more affected by heat are those taking certain medications, such as blood-pressure-lowing medications, antidepressants and some allergy treatments.

Maintaining stable temperature

Your normal temperature is around 37 degrees Celsius. Sweating is the way your body keeps itself cool so you can maintain a stable temperature on a hot day or during exercise.

Sweating is caused by glands found all over the body, which have ducts that open out onto the skin. These sweat glands are activated in response to heat (and stress).

But when you sweat, you lose fluid, and if you start losing more fluid than you are taking in, you become dehydrated. This means you won’t be able to sweat as much, reducing your body’s ability to bring your temperature down.

As well as regulating your body’s temperature, sweating helps control your fluid and salt balance. Upsetting this balance can have a range of consequences.

How heat harms?

High temperatures pose a health risk because your cardiovascular system has to work harder when it’s hot and for some people this extra strain can cause a heart attack or stroke, Dr Barnett said.

Extreme temperatures can also lead to a cascade of other changes in your body that can cause permanent damage to other vital organs, for instance there are often more admissions to hospital for acute kidney failure in those circumstances.

Heat exposure can manifest in a range of different ways including dehydration, heat rash, heat cramps, heat exhaustion and heat stroke.

Heatstroke is extremely serious and is often fatal. It occurs when your core body temperature goes above 40.5C and the body’s internal systems start to shut down.

Early signs of heat stress

Heat-related illnesses range from mild conditions such as heat rash or cramps, through to heat stroke, which can be fatal.

The effects of heat stress cascade, it’s important to know what the early signs look like.

Early signs of heat stress to look out for include:

headache
nausea
dizziness
weakness
irritability
thirst
and heavy sweating.

“The skin can be cold and clammy. Loss of salt from sweating can produce cramping. Anyone showing these symptoms should be taken to a cool place, rested and given cold drinks [no alcohol],” Dr Barnett said.

What is heat stroke?

Heat stroke occurs when the core body temperature rises above 40.5C and the body’s internal systems start to shut down.

There can be liver, kidney, muscle and heart damage and very often, the person’s nervous system is affected, resulting in delirium, coma and seizures.

The skin may be dry with no sweating and a person may stagger, appear confused, fit, collapse and become unconscious.

Every minute’s delay in cooling a person with heat stroke increases the likelihood of permanent injury or death.

Preventing heat stress and heat stroke

The following can help you avoid heat-related illness:

Drink water, lots of it: By the time you feel thirsty your body is already dehydrating, so drink keep having fluids even if you don’t feel thirsty. Avoid alcohol.
Dress comfortably: Lose, light-weight clothing helps your body stay cool. Light-coloured clothing reflects heat and sunlight.
Cool off: Take a cool shower or tepid bath if you’re feeling hot and flustered.
Avoid exposure: Stay out of the sun if possible. If not, wear a shirt, hat, sunglasses and sunscreen. Sunburn will affect your body’s ability to cope with the heat.
Seek air conditioning: If you don’t have air conditioning at home, spend the day somewhere that does, like a library, cinema or shopping centre. If you do have an air conditioner at home, make sure it has been serviced. Fans will also help you stay cool.
Keep your environment cool: Draw curtains, blinds and awnings early in the day to keep the heat out of your home.
If you or those close to you are suffering heat stress, call for help immediately: Symptoms of heat stress include extremely heavy sweating, headache and vomiting, confusion, swollen tongue.

This post originally appeared on ABC News.