Extreme heat is increasingly common in Australia and around the world and besides making us uncomfortable, it can harm our health . For example, exposure to extreme heat can exacerbate existing medical conditions, or cause problems such as heat stroke.
Authors
- Wen-Qiang He
Research Fellow in Biostatistics and Epidemiology, Faculty of Medicine and Health, University of Sydney
- James Smallcombe
Post-doctoral Research Associate, Faculty of Medicine and Health, University of Sydney
- Natasha Nassar
Professor of Paediatric and Perinatal Epidemiology and Chair in Translational Childhood Medicine, University of Sydney
- Ollie Jay
Professor of Heat & Health; Director of Heat & Health Research Incubator; Director of Thermal Ergonomics Laboratory, University of Sydney
Due to a combination of physiology and behaviour, children are potentially more vulnerable to severe heat-related illness such as heat stroke or heat exhaustion .
But these are not the only heat-related health issues children might experience on a very hot day. In a new study , we looked at emergency department (ED) visits and unplanned hospital admissions among children in New South Wales on heatwave days.
We found a significant increase in children attending hospital compared to milder days - with a range of health issues.
Why are children more vulnerable in the heat?
Sweating is the main way we lose heat from our bodies and cool down.
Children have a greater skin surface area to body mass ratio, which can be an advantage for sweating - they can lose more heat through evaporation for a given body mass. But this also means children can lose fluids and electrolytes faster through sweating, theoretically making them more susceptible to dehydration .
Meanwhile, younger children, particularly babies, can't sweat as much as older children and adults. This means they can't cool down as effectively.
Children in general also tend to engage in more outdoor physical activity , which might see them more exposed to very hot temperatures.
Further, children may be less in-tune to the signals their body is giving them that they're overheating, such as excessive sweating or red skin. So they might not stop and cool down when they need to. Young children especially may not recognise the early signs of heat stress or be able to express discomfort.
Our study
We wanted to examine children's exposure to extreme heat stress and the associated risks to their health.
We measured extreme heat as "heatwave days", at least two consecutive days with a daily maximum temperature above the 95th percentile for the relevant area on a universal thermal climate index. This ranged from 27°C to 45°C depending on the area.
We assessed health outcomes by looking at ED visits and unplanned hospital admissions among children aged 0-18 years from NSW between 2000 and 2020. This totalled around 8.2 million ED visits and 1.4 million hospital admissions.
We found hospital admissions for heat-related illness were 104% more likely on heatwave days compared to non-heatwave days, and ED visits were 78% more likely. Heat-related illness includes a spectrum of disorders from minor conditions such as dehydration to life-threatening conditions such as heat stroke.
But heat-related illness wasn't the only condition that increased on heatwave days. There was also an increase in childhood infections, particularly infectious enteritis possibly related to food poisoning (up 6% for ED visits and 17% for hospital admissions), ear infections (up 30% for ED visits and 3% for hospital admissions), and skin and soft tissue infections (up 6% for ED visits and 4% for hospital admissions).
We know many infectious diseases are highly seasonal. Some, like the flu, peak in winter. But heat and humidity increase the risk of certain infections caused by bacterial, viral and fungal pathogens.
For example, warmer weather and higher humidity can increase the survival of bacteria, such as Salmonella, on foods, which increases the risk of food poisoning.
Hot weather can also increase the risk of ear infections . Children may be at greater risk during hot weather because they often swim or play at the beach or pool. Water can stay in the ear after swimming and a moist environment in the ear canal can cause growth of pathogens leading to ear infections.
Which children are most vulnerable?
During heatwaves, we found infants aged under one were at increased risk of ED visits and hospital admission for any reason compared to older children. This is not surprising, because babies can't regulate their body temperature effectively and are reliant on their caregivers to keep them cool.
Our study also found children from the most disadvantaged areas were more vulnerable to heat-related illness on heatwave days. Although we don't know exactly why, we hypothesised families from poorer areas might have limited access to air-conditioning and could be more likely to live in hotter neighbourhoods .
Keeping kids cool: tips for parents
The highest levels of heat exposure on hot days for young children is usually when they're taken outside in prams and strollers. To protect their children from direct sunlight, parents often instinctively cover their stroller with a cloth such as a muslin.
However, a recent study from our group showed this actually increases temperatures inside a stroller to as much as 3-4˚C higher than outside.
But if the cloth is wet with water, and a small fan is used to circulate the air close to the child, stroller temperatures can be 4-5˚C lower than outside. Wetting the cloth every 15-20 minutes (for example, with a spray bottle) maintains the cooling effect.
When young children are not in a stroller, and for older children, there are a few things to consider to keep them cool and safe.
Remember temperatures reported on weather forecasts are measured in the shade, and temperatures in the sun can be up to 15˚C higher . So sticking to the shade as much as possible is important.
Exercise generates heat inside the body, so activities should be shortened, or rescheduled to cooler times of the day.
Sunscreen and hats are important when outdoors, but neither are especially effective for keeping cool. Spraying water on the child's skin - not just the face but arms, legs and even the torso if possible - can help. Wetting their hats is another idea.
Proper hydration on hot days is also essential. Regular water breaks, including offering water before, during and after activity, is important. Offering foods with high water content such as watermelon and orange can help with hydration too.
James Smallcombe receives funding from NHMRC
Natasha Nassar receives funding from NHMRC
Ollie Jay receives funding from National Health and Medical Research Council (NHMRC) and Wellcome Trust (UK).
Wen-Qiang He does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
