Explained: what this summer heatwave is doing to your body

How does your body cope in the heat?

That all depends on your own physiology, what kind of heat you're dealing with, and of course, what you're doing to help yourself.

In the midst of the heatwave sweeping the country, Aucklanders will be toiling in humidity levels of close to 90 per cent today.

A good measure of the sticky mugginess we feel is called dew point: this happens when temperature reached a point that, if cooled, saw water vapour from the air condensing on to a surface like grass.

This required 100 per cent relative humidity and occurred when the air temperature equalled the dew point.

We really began feeling clammy when the air was both warm enough to make us sweat - but carried enough water vapour to interfere with that process.

When temperatures rise, humans shed heat through the evaporation of sweat from our skin, which occurred smoothly when there's little moisture in the air.

But humidity compromised our ability to do so - which was why being in a rainforest was much more stressful on our physiology than a desert would be.

Because our sweat is essentially filtered blood - and it's the plasma of our blood that leaves through our sweat ducts - our bodies lose fluid that could have been used elsewhere, which leaves us feeling sapped of strength and energy.

Our bodies could adapt after just a few weeks of humid weather, by better balancing our fluids and sweating more efficiently.

But until that occurred, we found it harder to deal with mugginess than we otherwise might with dry heat.

A sudden change was enough to catch our biochemistry off-guard, and this could have wide-ranging effects on our body's normal biological cycle, or biorhythm, with implications for our mental, physical and emotional state.

Biorhythms rapidly disturbed by higher body temperatures could alter sleep quality and stress levels, and the demand of higher sweat rates and oxygen to shed heat energy, results in uncomfortable clamminess and losses of fluid.

People who worked outdoors or are required to wear stuffy uniforms might be noticing the change on their bodies more, especially if they aren't compensating with extra fluid intake.

Compounding the problem is the fact homes in the North Island generally have poor insulation, which makes them cold in winter, and too hot in summer.

Experts say those most vulnerable to the heat were elderly or pregnant people, or those who already had medical conditions.

Babies and children are also more at risk with rising heat, while healthy adults who work outdoors and those people who were in institutions like prisons, hospitals and residential care are also especially vulnerable.

"As we continue to see every year breaking new records for average and highest temperatures, climate change begins to take its health toll in the form of more days of extreme heat," said Dr Alex Macmillan, a senior lecturer in environmental health at the University of Otago.

"Even short-duration heat waves can increase deaths and hospital admissions from heat stroke, heart and lung disease, placing a heavy burden on families, communities and the health system.

"While New Zealand's high temperatures are not like those being seen in Australia, it's what our bodies are used to and our buildings are designed for that matters most."

And then there were another range of problems that came with disturbed sleep.

Trying to get to sleep two hours earlier than normal could be virtually impossible, as it went against the drive of our circadian body clock, and only left us feeling more frustrated.

And if the heat roused us awake in the middle of the night, one of the worst things we could do was reach for our tablets or smartphones to check the time.

The strongest source of information for our body clocks was light, so when we brought it into a time or environment we're not expecting, we could push our clocks back later.

Constant disruption to sleep could dog normal cognitive processes, slowing our reaction time, cloud decision-making, impede communication and make us more irritable and moody.

One just-published study even found that a single sleepless night was enough to ramp up the brain's pain-sensing regions and dumb down the areas that make pain more bearable.

What were the best ways to help ourselves?

Obviously, drinking lots of water - especially during exercise - helps us replenish that lost fluid.

And being somewhere with good air conditioning could help escape the clamminess.

Even getting out for a run – as long as we didn't overdo it – could help stimulate the adaptation your body needed to lose the heat quicker.

Christopher Holloway escapes the heat at Auckland's Point Erin pool yesterday. Photo / Doug Sherring

But in homes without air conditioning, getting to sleep could prove a struggle.

We slumbered best in ambient temperatures of between 13C and 23C, but first we needed to cool our core body temperatures enough to doze off.

For those who didn't have air conditioning, opening a window or turning on a fan were obvious options.

Another science-backed tip was taking a cool shower about 30 minutes before bed.

Looking back to the bigger picture, MacMillan said New Zealand simply remained unprepared for mean temperatures in the mid-30s.

"Hot, dry days also increase the health risk from bushfires, including burns and other injuries, as well as smoke-related air pollution impacts on lung and heart health," she said.

"As year on year we break new heat records as a result of our collective failure to act on climate change, New Zealand urgently needs a climate change and health adaptation plan, so that we can ensure people's health is protected from the impacts of climate change, including these higher summer temperatures.

"The good news is that by investing now in well-designed climate action, including homes and public buildings that are easy to cool without fossil fuels, and better city planning, we can stay healthier and more resilient to heat events like this, and reduce our climate pollution at the same time.

"Protecting health from increasingly severe heat waves requires New Zealand to be part of urgent global climate action."

How your body could be struggling

Brain: Higher body temperatures disturb our body's normal biological cycle, which regulates our physical health, cognition and emotions. It can lead to altered sleep quality can affect our reaction times and decision-making, and make us more irritable. Tip: Have a fan in the room.

Skin: We experience increased sweating to cool down, resulting in uncomfortable clamminess and losses of fluid. How much we might sweat depends not just on external temperatures but also our normal internal temperature, varies from person to person. Tip: Drink a lot of water to keep hydrated.

Circulation: The elderly, young and infirm could suffer from the results of poor circulation caused by rising temperatures. Symptoms include dizziness, dry skin, swelling and shortness of breath. It is caused by more blood being shunted to the skin and a loss of blood volume due to sweating. Tip: Try to keep cool and hydrate.

Heart & lungs: More energy and oxygen is required to dissipate the extra heat. This can leave us feeling fatigued as we've burned more calories, and also thirstier. Tip: Make sure you drink water.

*People may experience these effects when temperatures climb over 25C and humidity levels rise.