Heat stress occurs when the body is exposed to high temperatures and can no longer keep its internal temperature in check.
This is different from a heat wave – heat stress is about how the body reacts, not the weather itself.
Essentially, heat stress is the body's response to temperatures that exceed its ability to regulate.
It happens when the body cannot dissipate excess heat quickly enough to maintain a normal temperature.
Factors that influence heat stress:
The body tries to cool itself by sweating and dilating blood vessels. But sometimes that is not enough.
When these natural cooling mechanisms cannot keep up, heat stress can quickly become a problem. It can feel anywhere from slightly uncomfortable to truly dangerous.
A heat wave is a weather phenomenon – several days of unusually high temperatures. Heat stress is the body's reaction to heat, regardless of the weather forecast.
Heat waves make it easier to suffer from heat stress, but they are not the same thing.
You can actually experience heat stress even without an official heat wave, especially in workplaces where temperatures rise rapidly.
Practical differences:
Cities tend to be particularly affected during heat waves, as buildings and asphalt retain heat. Heat stress can also strike indoors, especially in industries or when wearing protective clothing that makes it harder for the body to cool down.
Heat stress affects the body in several ways, and it can lead to both acute and long-term problems.
Higher temperatures have been shown to increase the need for medical care and can even cause premature death, especially among older adults.
The body's reactions to heat stress:
Older individuals and those with certain illnesses are particularly vulnerable.
The body loses its ability to regulate temperature with age, making older adults especially susceptible.
If heat stress is not managed, it can develop into heat exhaustion or heat stroke. Common symptoms include dizziness, nausea, headache, and confusion.
In work environments where flame-resistant or heat-resistant clothing must be worn, the risk increases, as these often hinder the body's natural cooling.
Heat stress results from an interplay between weather, environment, and personal factors.
Climate change is making heat waves more common, and urban environments amplify the effect – especially for those already vulnerable.
Heat waves are the leading cause of heat stress in Sweden.
They are becoming more frequent and intense due to climate change.
Swedish conditions mean that temperatures rise during the summer. A heat wave is defined as at least five days with temperatures at least five degrees above normal.
Humidity exacerbates the situation, as sweat cannot evaporate as easily. This makes it harder for the body to cool down.
When it is also calm and sunny, it can become almost unbearable in certain workplaces.
Effects of climate change:
Cities often become heat islands where temperatures are higher than in surrounding areas.
Asphalt and concrete absorb heat during the day and release it slowly at night.
Building materials such as asphalt, concrete, and brick store heat. This means it can remain warm long after the sun has set.
Poor ventilation in buildings causes warm air to linger. Many older homes also lack modern insulation or air conditioning.
Industrial environments contribute to heat stress through:
Lack of trees and green spaces also means there is no natural shade or cooling.
Some individuals are more vulnerable to heat stress – this applies both due to age, health, and work environment.
Older adults over 65 often have a harder time regulating body temperature and may have chronic illnesses that worsen the situation.
Medical risk factors:
Occupational risks are significant for certain groups. Construction workers, welders, and industrial workers are exposed to high temperatures while often working physically hard.
Protective clothing made from flame-resistant materials limits the body's cooling. Necessary for safety, but it exacerbates heat stress.
Other factors:
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Heat stress can lead to both immediate and long-term health problems, affecting individuals of all ages.
Especially older adults and those with chronic illnesses are severely affected. Mortality increases significantly during heat waves in Sweden, and those already ill may experience worse symptoms and complications.
Heat stress can cause direct physiological effects that strike quickly as temperatures rise. Acute symptoms? We're talking about heat exhaustion, cramps, and in the worst case, heat stroke – this is not something to take lightly.
Direct health effects:
If exposed to high temperatures for extended periods, the body can begin to suffer internally. Kidney function deteriorates due to lack of fluids, and the heart has to work harder as the body tries to cool down.
Do you work in industry, construction, or logistics? Then the risk is higher, especially if you have to wear protective clothing in the heat. Flame-resistant clothing can make it difficult for the body to shed excess heat.
The Public Health Agency has shown that mortality spikes during heat waves in Sweden. It is quite clear: deaths increase by 10-15 percent when temperatures remain above normal for extended periods.
Risk factors for increased mortality:
Older adults are particularly hard hit, simply because their bodies have a harder time regulating heat. The ability to sweat and cool down decreases with age.
Social isolation and lack of access to cool spaces worsen the situation. Unfortunately, many older adults live in homes without proper ventilation or air conditioning.
Cities are the worst affected, where temperatures can be several degrees higher than in rural areas. The heat island effect in urban areas should not be underestimated.
Individuals with chronic illnesses often experience more severe symptoms when it is hot. Cardiovascular diseases are particularly sensitive as the heart has to work extra hard to cool the body.
For diabetics, heat can be a real challenge. Blood sugar levels can fluctuate unexpectedly, and insulin can lose effectiveness if not stored correctly.
Dehydration worsens glucose control and can lead to dangerous drops or spikes in blood sugar.
Particularly vulnerable groups:
Asthma and COPD often worsen when air quality declines during heat waves. It simply becomes harder to breathe when the air is warm and polluted.
Older adults with multiple chronic illnesses have almost no buffer left. The body cannot cope with the extra strain when the heat hits.
Some groups are clearly more susceptible to heat-related problems during heat waves. Older adults, children, individuals with disabilities, and those with chronic illnesses or specific medications need extra protection.
Older adults are the most vulnerable group when it comes to heat stress. With age, the body's ability to cool down deteriorates – less sweating and poorer blood circulation.
Physiological changes in older adults include:
Studies show that older adults have the highest risk of premature death during heat waves. The Public Health Agency emphasizes that this group needs special supervision and access to cooling.
It is not uncommon for older adults to live in apartments without good ventilation. Many do not even notice the early signs of heat stress, which can lead to help arriving too late.
Children are more sensitive to heat because they have a larger body surface area relative to their weight. They also produce more heat per kilogram and have difficulty adjusting their activity levels.
Small children cannot always communicate when they need water or cooling. They are entirely dependent on adults to protect them from heat.
Individuals with disabilities also have a higher risk of heat stress for several reasons:
This group needs individualized solutions and extra support.
Individuals with chronic illnesses are especially vulnerable to heat stress. Particularly cardiovascular diseases, diabetes, and depression increase the risk, according to several studies.
Medications that affect heat regulation:
Diabetes makes it harder for the body to sweat and regulate heat. Heart problems mean that blood circulation cannot keep up.
If you work with protective equipment in the heat, it becomes even tougher. Flame-resistant and heat-resistant clothing can severely limit the body's cooling – extra breaks and caution are required.
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Preventing heat stress involves combining smart indoor solutions, outdoor planning with greenery, personal choices, and of course, staying hydrated. It becomes increasingly important as temperatures rise.
How buildings are constructed significantly affects indoor temperatures. Sun protection such as blinds, awnings, or solar film can make a big difference and prevent heat from penetrating.
Ventilation systems must function properly to allow air to circulate when it is hot. Insulation of roofs and walls helps keep heat out and cool air in.
Fans and air conditioning are good complements when regular ventilation is not enough. Color choices for buildings matter – light colors reflect sunlight, while dark colors absorb it.
If you have old houses without modern insulation, you often have to resort to temporary solutions, such as draft-proof curtains or portable cooling units.
Smart urban planning can genuinely cool down urban environments. Trees provide shade and cool the air through evaporation, lowering temperatures by several degrees.
Green spaces and parks create cooler zones in the city. Water features such as fountains and ponds also help through evaporation.
Light paving materials reflect sunlight, while dark asphalt and concrete store heat. Material choices in public spaces significantly affect how warm it becomes.
Shading structures such as pergolas and awnings are invaluable on hot days. Ventilation corridors in urban planning facilitate air movement and reduce the heat island effect.
Clothing makes a significant difference when it is hot. Light, loose-fitting garments made of cotton or linen allow air to pass through and help sweat evaporate.
If you work in heat, you may sometimes need special clothing – cooling vests or materials that reflect heat can be invaluable. Flame-resistant and heat-resistant clothing is, of course, necessary if you are near hot surfaces.
Plan activities so that you avoid being outside during the hottest part of the day. Headgear and sunglasses are simple tricks that provide more protection than one might think.
Don't forget to take breaks in the shade or indoors – the body needs time to recover when temperatures soar.
Maintaining fluid balance is crucial for the body's natural cooling system. Water needs soar during heat waves, especially for older adults and children who are particularly sensitive to dehydration.
When we sweat, we also lose minerals, so electrolytes must be replenished. Fruits like watermelon and cucumber are really smart choices – they cool and hydrate at the same time.
Cooling methods? Yes, cold showers, ice on wrists and neck, or a wet towel over the forehead. Such tricks quickly lower body temperature by cooling the blood near the skin.
The Public Health Agency advises that we should drink water regularly, preferably before we even feel thirsty. It may seem excessive, but the body does not always signal in time.
Alcohol and caffeine? Not so good – they disrupt fluid balance and actually make it harder to stay cool. It is better to drink small amounts frequently than to gulp down a liter at once.
The Public Health Agency has developed quite comprehensive guidelines for managing heat stress in Sweden. Municipalities and property owners have also been given specific tasks to protect both residents and staff.
There are detailed action plans to protect us when heat waves strike. Climate change means we must adapt to higher temperatures and longer periods of heat.
The guidelines focus heavily on having early warning systems and risk assessments in place. How long the heat lasts, and whether nights are cool or not, affects health more than one might think.
Certain occupational groups are particularly vulnerable, according to the agency. Outdoor workers in agriculture, forestry, and construction, as well as emergency services and healthcare staff, need extra protection.
For industrial workers and welders, flame-resistant and heat-resistant work clothing is a must. This is not something to take lightly when it gets really hot.
The MSB has developed fact sheets and recommendations for municipalities during heat waves. It is about creating action plans that actually work when it gets really hot.
Municipalities need to:
Property managers have a special responsibility for indoor environments – after all, we Swedes spend most of our time indoors. Heat warnings often rely on outdoor temperatures, which do not always tell the whole truth about how warm it actually gets indoors.
Protective equipment and work clothing for logistics and construction workers must also be reviewed when it is hot. It is easy to forget, but it can make a significant difference.
There are several thermal indices and digital tools to measure and monitor heat stress. They help us assess risks and implement measures before it becomes dangerous.
WBGT (Wet Bulb Globe Temperature) is one of the most commonly used indices for measuring heat stress. It takes into account temperature, humidity, wind, and radiant heat – providing a good overall picture.
PMV (Predicted Mean Vote) and PPD (Predicted Percentage Dissatisfied) are mostly used indoors. PMV shows how people typically perceive temperature on a scale, while PPD indicates how many are likely to be dissatisfied.
PHS (Predicted Heat Strain) calculates physiological strain by analyzing body temperature and fluid loss. It is particularly useful in work environments where people are very active and it is hot.
Researchers have also developed models specifically suited for Swedish conditions. They take into account our climate and how we are used to handling temperature fluctuations.
ClimApp is a mobile app that aggregates several heat indices, including WBGT, PHS, PMV, and WindChill. It was developed within an EU project and is available for both Android and iPhone.
Web-based calculators make it easy to calculate PHS, IREQ, PMV, and PPD. No hassle with installation – just start using it directly in your browser.
Heat mapping uses satellite data and sensors to identify areas most affected by heat. Municipalities and organizations then gain better insight into where interventions are truly needed.
Many of these tools combine real-time data with forecasts. This allows for timely action before temperatures become critical.
People react differently to heat stress, and it is important to know what you can do in advance, which symptoms are serious, and how to quickly assist someone.
Older adults have a harder time regulating body temperature. They should stay in cool rooms when it is hot and avoid the sun during the hottest part of the day.
Regular contact with healthcare is especially important during heat waves. Healthcare personnel can monitor fluid intake and assist with fans or air conditioning.
Light and bright clothing makes it easier for the body to shed excess heat. It is wise to schedule activities for the morning or evening when it is cooler outside.
Profuse sweating that suddenly stops is a warning sign. Headaches and dizziness often come early.
If someone starts to feel nauseous or vomits, it may be heading towards heat stroke. If the person becomes confused or changes in personality, it is time to seek help immediately.
The skin may feel dry and warm when sweating has ceased. Rapid pulse and breathing indicate that the body is struggling to cope with the heat.
Creating shade in outdoor workplaces makes a big difference. Portable tents or fixed awnings provide a chance to rest in coolness.
Good ventilation helps the body shed heat through evaporation. Large fans or natural drafts can significantly lower temperatures.
Scheduling heavy work for the morning or evening reduces risk. Regular breaks in cool areas allow the body to recover.
Flame-resistant work clothing that still allows air to pass through is important for those working near heat sources. Specially designed garments can indeed be crucial in certain professions.
Move the person to shade or a cool room immediately. Remove excess clothing so the body can release heat.
Cold compresses on the neck, armpits, and groin cool the blood flowing close to the skin. It is smart to focus on these points.
Using a fan and spraying the body with lukewarm water provides quick cooling through evaporation. Ice water on the skin is not always best, as blood vessels may constrict and slow cooling.
Drinking regularly, both before and during heat exposure, is absolutely crucial. Sweat is the body's primary way to cool down – and it requires fluid.
During heavy sweating, electrolytes must also be replenished, not just water. Sports drinks or electrolyte solutions may be needed if one is outdoors for long periods in the heat.
Alcohol and caffeine make it harder to maintain fluid balance. Water remains the safest and simplest choice for most people.
Practical demonstrations of symptom recognition provide staff with concrete skills to identify heat stress in colleagues.
Role-playing and scenario training prepare them for real situations, which can truly make a difference when it matters.
Regular training sessions before warm seasons keep knowledge fresh and give new employees a chance to get into routines.
Safety briefings should definitely cover heat risk assessment and emergency procedures – it seems almost obvious, but it is still sometimes forgotten.
Distributing informational materials in multiple languages ensures that no one misses the risks, regardless of background.
Visual aids such as posters and small cards can be strategically placed in the workplace as simple but effective reminders.
The information on this page is intended as general guidance only and does not replace manufacturer instructions or applicable regulations. Workwise does not guarantee that the content is accurate, complete, or current and is not liable for decisions or actions taken based on this information. Always follow current standards and manufacturer instructions.