How do indoor environments impact physical and mental health?
People indoors (©2024 Let’s Talk Science)
People indoors (©2024 Let’s Talk Science)
How does this align with my curriculum?
Learn how temperature, humidity and carbon dioxide make us feel mentally and physically.
In Canada, people spend about 90% of their time indoors. This is why it is important to know how indoor environments affect mental and physical health.
Temperature
What is temperature?
Temperature is a measure of the thermal energy something has. Hot things have lots of thermal energy. Their atoms and molecules move very quickly. Cold things have less thermal energy. Their atoms and molecules move more slowly.
How do we measure temperature?
We often measure temperature using a thermometer. There are many different kinds of thermometers. We use thermometers to measure lots of different things. This includes our bodies and the air around us.
- Image - Text Version
Shown is a colour illustration with several different liquid, dial, digital and infrared thermometers.
The illustration is divided into four sections with different titles and objects on different coloured backgrounds.
The first section is yellow and titled “Liquid.” It has two long, thin, clear tubes marked with measurements. Both are half-filled with red liquid. The one on the left is mounted on a wood panel, and has a bulb full of liquid at the bottom. The one on the right has a blue casing and the bottom is a narrow blue stem. The descriptions below read, “Measures expansion and contraction of a liquid such as alcohol or mercury. Uses: Medical, indoor and outdoor temperature.”
The second section is pink and titled “Dial.” It has two round discs with red needles pointing to temperature markings. One has a long green stem, while the other appears to hang on a wall. The descriptions below read “Measures expansion and contraction of a coil of metal. Uses: Cooking, automotive, indoor and outdoor temperature.”
The third section is blue and titled “Digital.” It has two objects. One is a red box with an LED readout of 36.7 and a thin blue rod attached to it with a coiled blue cord. The other is a long green teardrop-shaped object with a silver metal top and a small, unreadable LED screen. The descriptions read, “Measures changes in electrical resistance. Uses: Medial, industrial, scientific.”
The fourth section is green and titled “Infrared.” It has a long, grey plastic object designed to be held in one hand. It has a bright red bulb on one side and an LED readout of 36.8 on the other. The description reads, “Measures infrared radiation coming off an object. Uses: Medical, industrial, scientific, firefighting.
Temperature Scales
People use different scales to describe temperature.
| Scale | Symbol | Where Used | Lowest possible temperature |
|---|---|---|---|
| Celsius | °C | Most countries | -273.15 °C |
| Fahrenheit | ℉ | United States, Liberia, Myanmar | −459.67 ℉ |
| Kelvin | K | Science | 0 (Absolute zero) |
Temperature (2015) Teacher's Pet (2:56)
How does temperature affect our health?
The human body works best when its internal temperature is between 36.1℃ and 37.2℃. Our bodies try to stay within this range. We call this thermoregulation. Thermoregulation is easier for some people than others. Children and the elderly can have trouble controlling body temperatures.
Did you know?
Normal body temperature is often given as 37℃ . But there actually is no “normal" body temperature. 37℃ comes from a single study done in the 1800s. Scientists now know that body temperatures are dropping.
When the environment you are in is hot, your body works to cool itself. When the environment is cold, your body works to warm itself.
Keeping Cool
When the air is hot around you, you sweat. Sweat is mostly water. When this water evaporates from your skin, it cools you down. Since you lose water when you sweat, it’s important to drink lots of water.
Some people may notice their skin gets redder when it is hot. This is because the blood vessels under your skin expand when it’s warm. Heat from the blood is transferred through your skin to the outside.
- Image - Text Version
Shown is a colour photograph of a student on a sports field, drinking from a bottle of water.
The student is wearing a neon green sports pinnie over a blue t-shirt. The sun is shining down on their face as they tip the bottle up to drink the last of the water. In the background, other students are visible standing near a fence.
Try this!
Mist water on one hand and keep the other hand dry. Blow on both hands. Which hand feels cooler? The wet hand should feel cooler. This is because water evaporates from it when you blow on it.
Some environments are so hot that they can cause heat stress. Heat exhaustion and heat stroke are both signs of heat stress. Heat stroke is also called hyperthermia. It happens when the body gets above 40 °C. An itchy rash, headache and upset stomach are early signs of heat stress. Heat-related illnesses can be very dangerous.
How Being Hot Makes Us Feel
In hot environments, the level of serotonin in the body drops. Serotonin is a chemical that carries messages between the brain and the rest of the body. It helps with eating, sleeping and your mood. Low serotonin levels can make you feel sad, tired, distracted and stressed.
A hot environment can also make it harder for you to learn. When your body sends more blood to your skin, it sends less blood to your brain! This can make it harder to focus on tasks and remember information.
- Image - Text Version
Shown is a colour photograph of a student holding one hand over their mouth while yawning.
The student is sitting at a small desk covered with different materials. All around and out of focus, other students can be seen at their own desks, using both hands to work with their materials. Posters and a bulletin board are mounted on the wall behind them.
Did you know?
Scientists in the United States found that students learned less when their school did not have air conditioning.
Keeping Warm
When your body is cold, it sends more blood to your internal organs. This keeps them warmer. Your hands and feet get less blood. This is why they tend to feel cold more quickly.
You might also shiver when it’s cold. Shivering is when your muscles shake due to cold. The movement of the muscles makes you feel warmer. You may also get goosebumps. This is when our body hair stands up. The hairs trap a layer of air near our skin. This air acts as insulation.
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Shown is a colour photograph of people in a dark room wearing winter clothes inside and reading books by candlelight.
An adult and a child sit at a kitchen table in a dark room. The child has their arms wrapped around themselves. The adult has one arm around the child. They are both wearing warm hats and scarves. They are both looking at a book open next to three burning candles. On the table nearby, two other books lie open.
Some environments are so cold that they can cause cold stress. Cold stress is the opposite of heat stress. Extreme cold can lead to frostbite and hypothermia. Frostbite happens when the body is exposed to freezing temperatures for a long time. Hypothermia happens when the body drops below 35°C. Both of these conditions range from mild to severe. Cold air can also increase the risk of picking up a virus and make asthma worse.
How being cold makes us feel
When people feel cold, they do things to try to get warm. This can include blowing on their hands or wiggling their toes. Doing things like this can make it hard to concentrate.
What is the best temperature for an indoor space?
In Canada, the ideal temperature range for indoor environments is 20 to 26℃. People find temperatures above and below this range uncomfortable.
Humidity
What is humidity?
Humidity is a measure of the amount of water vapour in the air. Water vapour is water in its gas state.
Misconception Alert
Many people think that steam is water vapour. It is not. Steam is tiny droplets of liquid water. If you can see it, it is liquid water!
How do we measure humidity?
We measure humidity using a hygrometer. There are many different kinds of hygrometers. Below are some examples of common ones.
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Shown is a colour illustration of a mechanical, a digital, and a wet bulb hygrometer.
The illustration is divided into three sections with different titles and background colours.
The first section is yellow and titled “Mechanical.” It has a round white dial with a red needle. This is marked with a scale labelled “% humidity.” The text below reads, “Measures expansion and contraction of a piece of organic material”.
The second section is pink and titled “Digital.” It has a square plastic object with three buttons and a large LCD screen reading 22℃ and 58%. The text below reads, “Measures changes in electrical resistance using a semiconductor.”
The third section is blue and titled “Wet bulb (psychrometer).” It has two glass thermometers mounted on a brown rectangular plaque. The one on the left is labelled “Dry.” The one on the right is labelled “Wet.” Both are half-filled with red liquid. The bulb of liquid at the bottom of the dry one is visible. The bulb on the wet one is wrapped in beige material. This is labelled “Cloth wick” and is dipping into a blue section below labelled “Water container.” The text below reads, “Measures the difference between the temperature of a wet thermometer and a dry thermometer.”
Measurements of Humidity
We can describe humidity in several different ways.
- Absolute Humidity (AH)
This is the amount of water vapour in the air. It is the number of grams of water per square metre of air. Absolute humidity does not depend on air temperature. - Relative Humidity (RH)
This is the amount of water vapour in air compared to how much it could hold. Unlike absolute humidity, relative humidity depends on temperature. Since it compares two amounts, we can represent it as a percentage (%). Look at the drinking glasses below. Imagine that the liquid water is water vapour.
- Dew Point
This is the temperature at which air has 100% RH. At temperatures below this point, water vapour becomes liquid water. This water could be dew or another type of precipitation. - Humidex
This is how air temperature feels because of humidity. We calculate it using the temperature and the dew point. For example, imagine that the temperature is 30℃ and the dew point is 15℃. Using a humidex chart, we would find that the humidex is 34℃. You can use this Government of Canada online calculator to find out the humidex.
Did you know?
Humidex is a measurement only used in Canada.
How does humidity affect our health?
What happens when humidity is high?
Humidity influences how people feel temperature. When the air is humid, it feels warmer to us. When the air is very humid, it can feel sticky and uncomfortable. Very high humidity levels can be bad for our health.
Remember that the body tries to keep to a certain temperature. When it gets hot, it tries to cool itself by sweating. Sweat transfers heat and water vapour to the surrounding air. But when the air is very humid, the water in sweat cannot evaporate. This means that our body cannot cool itself. High body temperature can cause physical and mental health problems.
High humidity can also make things around us damp. This includes towels, furniture, paint and flooring. Mould, bacteria and dust mites thrive on damp things. These tiny organisms can cause allergies and make respiratory illnesses worse.
High humidity has also been shown to make some mental health conditions worse.
- Image - Text Version
Shown is a colour, microscopic photograph of dust mites on white fibres dotted with their feces.
The mites are crawling along thick, tangled white strands. They are about the same width as the stands. The mites are brownish-pink oval shapes with thin legs. All of the fibres are sprinkled with tiny brown dots. These are the mites’ feces.
What happens when the humidity is too low?
Air with low humidity is also known as dry air. Like humid air, dry air can make us feel uncomfortable. Dry air can cause dry lips, cracked skin and itchy eyes. It can also make some types of allergies worse.
Dry air can also help spread viruses. When people cough or sneeze, they send droplets into the air. These droplets can contain viruses. When the air is humid, the droplets pick up water. They get bigger and fall to the ground. When the air is dry, the droplets do not pick up water and stay small. This lets them float around in the air, ready to infect another person.
- Image - Text Version
Shown is an illustration of a person coughing into their hands and droplets floating of water containing viruses floating in the air.
The person is out of focus in the background on the left. They are hunched over with both hands covering their mouth. Water droplets escape between their fingers and float out into the air. These grow in size and are in focus in the foreground. The spheres are filled with viruses, which are represented as pink circles covered in spikes.
What is the best level of humidity for an indoor space?
According to Health Canada, indoor RH should be between 30 and 50%. In this range, mould and bacteria are less likely to grow and dust mites cannot survive. Viruses are also less likely to infect people. Research has shown that in this range, students get sick less and miss less school.
What is carbon dioxide?
Carbon dioxide is a molecule with one carbon atom and two oxygen atoms. This means it has the chemical formula CO2. People often call it by this name.
At room temperature, carbon dioxide is a gas. It has no colour, no smell, and does not easily catch on fire.
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Shown is a colour illustration of a carbon dioxide molecule.
In the centre is a red sphere. It has the label “C”. This represents a carbon atom. Connected to the carbon horizontally on its left and right side are two thick black lines. These represent double molecular bonds. Connected to each set of lines are blue spheres. The spheres each have the label “O”. These represent oxygen atoms. Below the diagram is the label “COsubscript2”.
Did you know?
Fire extinguishers use liquid carbon dioxide. We call solid carbon dioxide dry ice.
How do we measure carbon dioxide?
People measure CO2 using a carbon dioxide sensor. There are many different types. A common type is the nondispersive infrared (NDIR) sensor.
It measures how much light the CO2 in a sample of air absorbs. The sensor has an infrared light at one end. It uses infrared because carbon dioxide absorbs infrared light. The light travels through a sample of air to an infrared detector.
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Shown is a colour photograph of a carbon dioxide sensor showing carbon dioxide reading of 735 PPM.
The sensor has a white plastic case on which is printed “CO2 Monitor” on the left side. In the top right corner is a grey LCD screen with black numbers. Along the edge of the screen are three small lights. The bottom green light is on.
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Shown is a colour diagram of infrared light shining through carbon dioxide molecules inside a CO2 meter.
The diagram shows a long rectangular chamber. Along the top left side is an opening labelled “Air in”. Along the bottom left is an opening labelled “Air out.” Circles labelled “CO2” float from the first opening, through the chamber to the second. In the left end of the chamber is a red bar. It represents an infrared light source. Red colour spreads from here toward the other end. This is labelled with a red arrow and the words “Infrared light.” In the right end of the chamber is a blue bar labelled “Infrared detector.” A curved black line leads from this end of the chamber to a grey rectangle outside the chamber. This represents a digital display. Text on the rectangle reads “600 ppm.”
The detector measures how much light reaches it. It subtracts this from the original amount of light. The amount of light that reaches the detector is proportional to the number of CO2 molecules in the air. The number of molecules is the concentration of CO2 in the air. Concentration is measured in parts per million (ppm). The sensor converts the concentration and displays it on a screen.
How does carbon dioxide affect our health?
Carbon dioxide is in the air around us all the time. But if CO2 levels are high, it can impact our physical and mental health.
How do high CO2 levels make us feel?
The normal carbon dioxide concentration in outdoor air is between 300 and 500 ppm. Indoors, this level can get much higher. At higher CO2 levels, people can feel tired. They may get headaches and have faster heart rates. They may also feel confused or have trouble making decisions and solving problems. At very high levels (20 000+ ppm) the body does not get enough oxygen. This can lead to a loss of consciousness and in extreme cases even death.
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Shown is a colour bar graph that represents air quality at different CO2 levels.
The Y axis is labelled “Carbon Dioxide Concentration (ppm).” This goes from 0 at the bottom to 5000 at the top. The bar is divided into different coloured sections. These colours are labelled across the bottom. The section from 0-300 ppm is green, which means “Good Air.” Above, the section from 300-1000 ppm is yellow for “Acceptable Air.” From 1000-2000 ppm is orange for “Poor Air.” From 2000-5000 ppm is red for “Very Poor Air.”
Scientists have studied how CO2 levels impact students in schools. They found that students in classrooms with lower CO2 concentrations had higher test scores and fewer absences. And it isn’t only students that CO2 levels affect. Teachers also feel the effects of CO2.
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Shown is a colour photograph of students in a classroom, looking tired.
Six students are sitting at a row of desks. They have their books open but they are not paying attention. One is leaning their head on their hand. Another has their head down on their desk with their eyes closed. Behind, other students are yawning, rubbing their eyes, and staring off into space.
What is the best level of carbon dioxide for an indoor space?
The government of Canada recommends that indoor CO2 levels should not be 1000 ppm or more for more than 24 hours. In general, the closer the CO2 level is to that of outside air, the better.
Now you know how and why heat, humidity and carbon dioxide affect mental and physical health.
- Answer
If there are 22 grams in the air, the RH is 100%. If it contains 11 grams, or half the maximum amount, the RH is 50%.
Learn more
Introduction to Homeostasis and Regulation (2021)
In this Let’s Talk Science backgrounder, learn about homeostasis and how it regulates temperature, blood pressure, blood pH and blood sugar.
Heat: Indoors and Outdoors (2024)
This backgrounder by Let's Talk Science explores the importance of heat, its sources and how people control it indoors.
Humidity: Outdoors and Indoors (2024)
In this backgrounder by Let’s Talk Science, learn about the importance of humidity, its sources and how people control it indoors.
Carbon Dioxide: Indoors and Outdoors (2024)
This backgrounder by Let’s Talk Science explores the importance of carbon dioxide, its sources and how people control it indoors.
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