The pros and cons of air conditioners for our health

Last week it has been warmer in large parts of Europe than it has ever been in the past 50-75 years. You might think that it has never been this hot in our living memory, but consider that we have only been able to reliably measure the outside temperature for about 100 years.
This means we cannot properly assess whether it has not been much warmer in the more distant past. What we do know is that Europe has gone through periods of extreme drought, with large rivers drying up. We have not yet experienced that situation in our current lifetime.

Anyway, the fact is that it is warmer than we have experienced in a long time and it is not very convenient when you live in a small apartment with large south-facing windows, which can cause temperatures to rise enormously.

As you may have guessed, we installed air conditioning in our company building when a short holiday turned out to be disastrous for part of the stock. In addition to keeping the stock room at a constant temperature between 15 and 25 °C, a dehumidifier also ensures that the humidity does not exceed 50%.
This allows us to guarantee consistent quality of all our supplements.

However we had not taken into account was the fact that we would also need cooling ourselves.
Fortunately the air conditioning works well enough to also cool the adjacent rooms, but it could have been better because it does not reach the ground floor, although it will probably make a difference of a few degrees.
On the ground floor we ensure that the office space does not heat up too much by using reflective foil and thick curtains. A table fan provides individual cooling.

However, a less pleasant experience remains the enormous transition between the outside temperature that rose above 35°C and cooled indoor spaces of 20°C. This was especially the case after a sweaty bike ride, when I contracted mild pneumonia and have been plagued by coughing fits for a week.

Since the pros and cons of air conditioning have led to heated discussions in recent days, I think it is about time to inform you about the health advantages and disadvantages of air conditioners.

Europe’s deadly aversion to air conditioning

Europe is warming about 0.5°C per decade since the 1980s. The continent’s annual count of days since 1950 with “strong heat stress” — a feels-like temperature of 32°C or higher was flat from the 1950s into the 1980s, then rose sharply: 2022 through 2024 rank as the highest on record.

Heat mortality has also been increasing in Europe with a high of approximately 68,000 heat-related deaths in 2022. The WHO European Region reports that heat mortality is up by about 30 percent over two decades.

Europe largely chooses these deaths through a long resistance to a 1902 invention that the rest of the rich world treats as an incredible benefit of modern technology — air conditioning.

If Europe had air conditioner penetration approaching levels of the U.S. or Japan, what would we expect the effects to be on heat mortality?

Richest, coolest, deadliest

A continent that enjoys both comparative wealth and, by latitude, fewer hot days than most inhabited regions nonetheless records the world’s highest per capita heat-death rate.
Age explains some of it — but the United States and Japan also have aging populations and yet have far fewer heat-related deaths.

A more important difference: air conditioning: European household penetration sits near ~19%, versus ~76% in North America and more than 90% in Japan.

The counterfactual

American states were tracked over time, before and after air conditioning spread, with the local climate held constant.
Increased AC penetration caused the drop in the risk of dying on an extremely hot day by about 75% .

The math is simple. Today’s heat deaths reflect today’s level of AC coverage.
Raise the coverage, and a share of those deaths are eliminated — in proportion to how protective AC is and how many more households gain it.

If Europe had AC penetration similar to North-America (76%) in the summer of 2022, then the continent would have avoided ~26,000 heat deaths in a summer like 2022.
With near-universal coverage (90%) ~35,000 deaths would have been avoided.
Even a modest coverage of 40%, which is below today’s Spanish or Italian levels, this would still save something like 6,000 to 8,000 lives a year.

Age matters

Heat deaths concentrate almost entirely among the old. The over-80s alone account for about two-thirds of European heat deaths, and the over-65s for about 93%.

The risk climbs steadily with age.
For a 65-year-old, extreme heat lifts those odds by about 21%; for an 85-year-old, by 27%.
Extreme cold is harsher still, raising the odds by 21% at 65 and 36% at 85.

Based on studies from the U.S. and Canada, the typical European heat victim is an older adult, often over 80, with cardiovascular or respiratory disease, living alone in poorly insulated housing. Most die indoors, at home.

New York City’s health department, reviewing medical-examiner records of heat-stress deaths, found that 89% of decedents had at least one chronic health condition, most commonly cardiovascular disease.

British Columbia’s coroners service, reviewing the 619 deaths from the 2021 heat dome, found that 98% occurred indoors, 67% of the dead were 70 or older, 56% lived alone, and 93% had no air conditioning.

The AC’s protective effect fell most heavily on the very groups most exposed — infants and the elderly.

In Europe, over-65s account for about 93% of heat deaths, so a focus on cooling that group first would capture nearly the entire avoidable death toll.
Equipping care homes, hospital wards, and the homes of old folks would deliver most of the benefit at a small share of the cost of providing AC everywhere. Europe does not need air conditioning in every home or office to save the many thousands of lives.

Where lives can be saved

The cooler northern countries combine large populations, lower heat-death rates, and very thin AC coverage, so they supply a surprisingly large share of the avoidable deaths — it is not just the Mediterranean.

Germany — at 3% household AC, the U.K. — at 5%, and France — at 25%, each show potential for more avoidable deaths than hotter Greece, with ~66% AC penetration.

The countries with leaders that most loudly champion passive cooling and energy restraint — notably Germany, the U.K. and France — have the most potential for saving lives through expanding AC.

The policies that block AC

Europe high heat mortality risk and lower penetration of AC reflect policies that actively deter cooling. Some of these policies are at the EU level, and some are at the national or sub-national level.

These polices are reflective of an energy-degrowth ideology — one that treats every kilowatt-hour as a vice rather than a virtue for improving human lives:

These regulations have not happened by accident, but they come from an ideology that emphasizes energy degrowth as the only viable solution to climate change. What that means in practice is that Europe has heavily prioritized insulation and passive cooling.
In contrast, active cooling through an AC, even if running on clean (nuclear) energy, has been disincentivized because it requires energy.

EU gas regulations: cuts HFC refrigerant supply by 80% by 2030 and to zero by 2050; bans servicing AC units from 2026 onwards.
Proposal: carve out an exemption tied to health and accelerate approval of natural refrigerants so units stay serviceable.

EU energy performance of buildings: rates dwellings by its energy use. An installed AC unit lowers the rating so landlords avoid or remove units.
Proposal: score cooling for health benefit, not just energy use and stop letting AC drag a building into a banned class.

Energy labels in France (and the NLs): bans rental of the worst-rated dwellings on a rolling schedule. AC can tip a unit into a forbidden grade. 
Proposal: excempt efficient cooling from the rating penalty.

Geneva AC permit: requires an exceptional permit and proof of medical necessity before installing a fixed AC; roughly 4 housing permits approved per year.
Proposal: replace prove the need permitting with a default right to install efficient cooling.

Spain/Italy public thermostat caps: bar cooling below 27°C in offices. Hot enough to dull cognition
Proposal:drop the caps during heat alerts and exempt care homes, wards and schools.

What about Europe’s commitment to climate goals?

Setting aside the benefits of saving lives, expanded penetration of AC would not necessarily undo the continent’s commitment to achieving net zero.

Air-conditioning demand peaks during the day and evening: during the 2025 heat waves France (with little AC), saw evening electricity peaks about 25% above its off-season average, while air-conditioned New York ran 90% higher.
Higher, but not impossibly so. France already runs a grid that is largely decarbonized, it would simply need more of what it already has. And air conditioning demand matches well with the time of day when solar energy is most readily available.

Consider also that electrifying cars and home heating is projected to raise European electricity demand by, lifting total demand by some 40% — what the EU has formally committed to under "Fit-for-(20)55".
Increasing demand for electricity to power AC in the context of this huge buildout seems very doable.

The larger problem is not technology or cost, but the fact that among many, cooling technologies have taken on a moral framing as a vice.

The bigger issue: adaptation optimism

Climate advocates have long disparaged adaptation — they cast it as an avoidable cost of failed mitigation, dismiss its effectiveness, and treat it as an obstacle to emissions cuts. We argue that this framing inverts reality.

Adaptation, especially through economic development, drives most climate-sensitive outcomes on the space and time scales that affect people living today. Crop yields, affluence, and death rates from climate hazards have improved across almost all regions over recent decades, despite climate change, because development and adaptation pulled them in beneficial directions faster than any growth in impacts from changes in climate.

Adaptation costs and benefits are typically close in time and space. Mitigation, by contrast, spreads benefits across regions and generations, and can even erode adaptive possibilities. Adaptation and mitigation are not trade-offs. Europe and its approach to AC might just be the poster child for getting this wrong.

What are the downsides of airconditioning?  Five hidden health risks everybody should know

Millions of people transition from chilled offices to icy cars and eventually to cooled bedrooms, often spending upwards of 20 hours a day in climate-controlled environments. However, while escaping the heat provides immediate relief, this constant reliance on artificial cooling may be silently compromising physiological well-being. The statistics are revealing and cause for concern and need to be kept in mind as the heatwave may be hard to deal with but how you choose to deal with it should be rooted in science.

Clinical research indicates that individuals spending significant time in air-conditioned environments report a 50% higher rate of respiratory symptoms compared to those in naturally ventilated spaces.

Occupants of buildings with central air conditioning exhibited significantly higher symptoms of "Sick Building Syndrome" (SBS), which is a condition where people experience acute health effects linked to time spent in a building, than those in buildings with natural ventilation.

1. A breeding ground for pathogens

Air conditioning (AC) units, particularly central cooling systems, act as massive moisture traps. When warm air passes over the cooling coils, condensation forms. If maintenance is neglected, this moisture does not drain properly, turning the unit into a reservoir for bacteria, mould, and fungi.

Legionella bacteria thrive in the standing water of cooling towers and AC ducts. When the unit is turned on, these pathogens are aerosolised and inhaled. This can lead to Legionnaires' disease, a severe and potentially fatal form of pneumonia.
Beyond bacteria, mould spores circulating through dirty vents can cause persistent allergic reactions and chronic sinus infections that often go misdiagnosed as simple "seasonal allergies".

2. Chronic dehydration and dermatological impact

The fundamental physics of an AC unit involves extracting moisture from the air to lower the temperature. Unfortunately, the machine cannot distinguish between atmospheric moisture and the moisture in the human body.

Dry Eye Syndrome: the constant flow of dry air accelerates the evaporation of the lipid layer of the tear film. This results in redness, irritation, and blurred vision, which is particularly harmful to contact lens wearers and those already prone to digital eye strain.

Skin barrier damage: low humidity levels strip the skin of its natural oils. Over time, this leads to trans-epidermal water loss, causing itchiness, flaking, and the worsening of pre-existing conditions like eczema and psoriasis. The skin's ability to heal itself is significantly slowed in a low-humidity environment.

3. Respiratory irritation and asthma triggers

The air inside an AC room is often "dead air" as it is recirculated rather than refreshed. This means the concentration of pollutants can actually be higher indoors than outdoors.

If AC filters are not cleaned every 15 to 30 days, individuals are essentially breathing in recirculated dust, pollen, and mould. This recycled air is a primary trigger for sudden asthma attacks, chronic rhinitis, and even hypersensitivity pneumonitis." For those with sensitive airways, the cold air itself can cause 'cold-induced bronchospasm, leading to shortness of breath and wheezing.

4. The "thermal shock" phenomenon

When temperatures go well over 40°C which is quite common in African and Asia, it is common to walk from a 45°C outdoor environment directly into an 18°C office. This 27-degree difference creates "thermal shock". The human body's thermoregulation system is forced into overdrive to maintain internal homeostasis.

This rapid transition causes blood vessels in the skin and nose to constrict suddenly, which can weaken the local immune response in the nasal mucosa.
Consequently, the body becomes more susceptible to viral infections, including the common cold and influenza. The physical stress of constant temperature shifting also leads to "summer chills" and muscle stiffness.

5. Persistent fatigue and neurological symptoms

Evidence suggests a strong link between prolonged AC usage and increased lethargy. A study conducted by the University of Helsinki associated AC environments with neurological "sick building" symptoms. These include persistent "heavy-headedness", headaches, and unexplained fatigue.

This is often attributed to the lack of fresh oxygen exchange. In a closed AC room, carbon dioxide levels rise steadily. High concentrations are known to impair cognitive function, reduce concentration, and cause a general sense of malaise. Many office workers attribute their afternoon slump to a heavy lunch, but the culprit is frequently poor air quality from the HVAC system.

Another few advantages of airconditioners

1. Boosts metabolism
Studies show more time in cold weather may help you lose weight. Your body may develop a greater amount of healthy, energy-burning “brown fat” as it deals with more frigid air. Air conditioning in hot weather can help keep you in a cool state, but you’ll also have to lower your indoor temps in the winter to below 18°C see a real benefit.

2. Helps cognition
A 2018 Harvard study showed that students who lived in dorms without AC during hot summer months did worse on cognitive tests than those who had cool central air.

3. Improves sleep quality
Experts say sleeping in a room that’s between 15-19°C is ideal for the best rest. This is because your body cools down as part of a natural sleep cycle, so a cool room helps that happen. Sometimes AC is the tool you need to get your sleep space to the right temp.

And above all:
4. Saves lives during heatwaves!
Air conditioning may come with some negative effects, but there’s no doubt it can be lifesaving when temperatures soar. Once your body temperature goes above 39°C, you’re at risk of heat exhaustion -- nausea, cramps, dizziness, feeling faint -- and if you continue to heat up, you could get heat stroke.

Guidelines for safe cooling: protecting your health

To mitigate these risks, it is not necessary to abandon air conditioning entirely. Instead, a more mindful approach to cooling should be adopted:

The 24 -degree Celusis rule: maintaining the AC at a moderate temperature (24°C-26°C) minimises the impact of thermal shock and keeps the humidity at a more biologically acceptable level.

Periodic ventilation: for every four hours of AC use, the unit should be turned off, and windows opened for 15 minutes. This allows for necessary carbon dioxide exchange and introduces fresh oxygen.

Active hydration: increased water intake is essential. The body loses moisture in dry, cooled air even in the absence of thirst. Herbal teas and water-rich fruits can help maintain the skin's hydration from the inside out.

Rigorous filter hygiene: cleaning AC filters every two weeks during peak summer is mandatory. Professional deep cleaning of the cooling coils and drainage trays should be done at the start of every season to prevent microbial buildup.

Use a humidifier: If skin and eye dryness are persistent, using a small tabletop humidifier can return essential moisture to the immediate environment.

So, the heatwave may force you to blast the AC, but it is essential that you follow the guidelines to set the temperature, which doesn't send your body into shock or expose you to health risks that damage your well-being.

Summary

Europe is experiencing more frequent and intense heatwaves, with rising heat-related deaths—around 68,000 in 2022—largely due to low air conditioning adoption (~19% household penetration vs. 76% in North America and over 90% in Japan).
Studies show AC could prevent tens of thousands of deaths annually, especially among the elderly and those with chronic conditions, by reducing indoor heat stress.
It also improves cognition, sleep quality (optimal at 15-19°C), and may support metabolism through brown fat activation.
In workplaces and homes, it protects stock, productivity, and vulnerable populations.

However, rapid temperature shifts (e.g., 35°C outside to 20°C inside) can cause “thermal shock,” leading to respiratory issues like pneumonia.

Poorly maintained units foster bacteria (e.g., Legionella), mold, and allergens, worsening Sick Building Syndrome, asthma, sinus problems, and infections.

Dry air causes dehydration, dry eyes, skin irritation, and fatigue from reduced fresh air and rising CO₂ levels.

Safe use guidelines: set AC to 24-26°C, ventilate regularly, clean filters bi-weekly, stay hydrated, and use humidifiers. AC saves lives during extremes but requires mindful maintenance to avoid health trade-offs.
Balanced adoption, focused on care homes and high-risk groups, offers major benefits without undermining energy saving goals.