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Does Hot Air Have Less Oxygen?

It can be tough to catch a breath on hot summer afternoons. But during the crisp autumn months, the cool air feels refreshing and is much easier to breathe. Does this mean we’re inhaling less oxygen for every breath of hot air?

Hot air does have less oxygen than cold air in an equal volume. The higher the air temperature, the faster molecules move. In other words, oxygen molecules are further away from one another, leading to a decrease in air density.

The rest of this article will provide more information on the air we breathe, the effects of breathing in hot vs. cold air, and what makes it difficult to breathe in hot air. I’ll also share a few tips to help you get enough oxygen throughout summer.

What Is in the Air We Breathe? (Percentages)

Air is a mixture of various gases in the Earth’s atmosphere, the biggest percentage of gases being nitrogen at 78% and oxygen at 21%. There are also trace amounts of other gases, such as hydrogen, carbon dioxide, and helium. 

The approximate proportions of gases listed by percentage per volume in the air are represented in the following chart from Encyclopaedia Britannica:

Type of Gas Percentage
Nitrogen 78.084%
Oxygen 20.946%
Argon 0.934%
Neon 0.0018%
Helium 0.000524%
Methane 0.0002%
Krypton 0.000114%
Hydrogen 0.00005%
Nitrous Oxide 0.00005%
Xenon 0.0000087%

Air also holds a lot of solid particles are called aerosols. Some aerosols are picked up naturally by the wind, such as dust and pollen. 

However, air can also carry tiny particles from pollutants like a car’s exhaust or a power plant. Even if the air looks clear, you’re still inhaling millions of solid aerosol particles. Despite their minuscule size, aerosols have major impacts on air quality and health.

Water in the atmosphere is called water vapor. High levels of humidity indicate there is a lot of water vapor. 

Depending on the temperature, humidity levels range from about 40–50% in the middle of winter to very humid (up to 100%) in tropical climates. 

More precisely, at 86°F (30°C), air can contain up to 4% of water vapor by volume. 

On the other hand, air cooled to a temperature of -40°F (-40°C) can contain only up to about 0.2% of water vapor by volume. 

So, the higher the temperature, the more humidity in the air. As the temperature cools down, the air holds less water vapor because it turns back into a liquid.

Cold vs. Hot Air

Air is made up of molecules that are constantly in motion. When air warms and gets hotter, it absorbs energy in the form of heat. This absorbed energy makes the molecules move faster and bump into each other.

Because each molecule requires more space, the air expands, becoming lighter and less dense. The same number of molecules in the warmer air now takes up a larger area. Alternatively, it increases air pressure in an airtight enclosure.

On the other hand, cold air has the opposite reaction. Cold air is denser than hot air because the molecules are closer together. The bonds in cold air also absorb less energy, so the molecules have less movement than hot air. 

When the temperature drops, the molecules move slower and take up less space while reducing the air pressure.

Because of various molecule movements, cold air weighs more and sinks, driving hot air upwards because it’s less dense. 

The only caveat is the vapor buoyancy effect, where despite being at the same temperature, pressure, and volume, humid air is lighter than dry air.

Why Is Hot Air Stuffy and Hard to Breathe In?

When the temperature creeps up and humidity levels are at an all-time high in summer, your body needs more energy to remain cool.

Hot air can also irritate your airway, causing you to feel a tightness in the chest and shortness of breath. If you have asthma or chronic obstructive pulmonary disease (COPD), it’s even more difficult to catch a breath in extreme weather conditions.

When the air becomes warmer, water molecules also heat up, giving them more energy. Remember, air is filled with different gases and water vapor. Warm air contains more water molecules than cool air. 

These energized water molecules are less likely to condense than the water molecules in cold air.

The capacity of air to hold water vapor increases with the temperature.

There is less oxygen to breathe in humid air, even though water vapor technically contains oxygen molecules. Since there is a higher water vapor content and fewer oxygen molecules, breathing in the hot, humid air is hard. In turn, this can cause humidity breathing anxiety, classified as a vasovagal attack. It triggers symptoms similar to a seizure caused by extreme heat exposure. 

Extreme temperatures and high humidity levels can also cause air to become stagnant. This means that there are pollutants and various allergens such as fungus and mold in the air, causing a flare-up of asthma. 

Researchers at John Hopkins University conducted a study that concluded an increase in the severity of COPD symptoms with higher outdoor temperatures and higher indoor temperatures.

The higher the humidity levels, the fewer oxygen molecules are left to inhale. This causes an inadequate oxygen intake, even if you breathe slowly and deeply. 

So, if you find yourself in a confined spa with a boiling water source and lots of steam, you’ll find it difficult to breathe.

How to Get Enough Oxygen in Hot Weather

Hot weather, allergies, pollution, and humidity can make it difficult to breathe in summer, but it doesn’t mean you need to stay indoors. 

You can enjoy even the hottest summer days with some practical precautions, such as the following:

  • Listen to your body and give it time to adjust to the heat.
  • Limit outdoor physical activity, or plan activities during the early mornings and late evenings.
  • Check your local air quality report and plan your activities depending on the forecast.
  • Avoid any triggers that may make it hard to breathe, such as smoking and pollution.
  • See a doctor and mention any concerns about respiratory irritants.
  • Use medications as needed or prescribed.
  • Stay hydrated.


There are many differences between hot and cold air at a molecular level. Hot air has less of every gas in an equal volume as cold air, including oxygen. This is because molecules move and expand when they get hot. Consequently, warm air takes up a larger area as it becomes less dense. 

We inhale different gases, water droplets, and solid particles in every breath we take. It can be very difficult for people to breathe in extreme heat.

Humidity is another major factor that affects oxygen levels in hot weather.


  • Chris Hewitt

    Chris is a Texas-based freelance writer who loves the outdoors and working in his garage. When he's not enjoying the Texas sun, he can be found tinkering with all sorts of things in his workshop.

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