What is humidity? Why measure & what your levels mean

WHERE DOES HUMIDITY
COME FROM?

Humidity is a natural part of our atmosphere, it comes from the amount of water vapor in the air. Water vapor enters the atmosphere by evaporating from the large bodies of water on the Earth’s surface including lakes, oceans, and seas.

DID YOU KNOW:

97%¹ of the Earth’s water can be found in our oceans².

It is an integral part of the water cycle, as water vapor is continuously generated by evaporation and removed by condensation. When the temperature is higher, the air can hold more water vapor, meaning that the warmer the climate, the higher the humidity level can be.

For example, a densely saturated amount of air may contain 28 grams of water per cubic meter at 30°C, but only 8 grams of water per cubic metre of air at 8 °C³.

HOW TEMPERATURE
AFFECTS INDOOR
HUMIDITY
LEVELS

Colder air cannot handle as much moisture as warmer air. Temperature in relation to humidity is important, especially as we spend 90% of our time indoors. Consider for example a winters day. The outdoor air could have a 100% relative humidity at 5°C, and therefore contain 6.8 grams of water. Indoors however, 5°C would be very uncomfortable, so we would warm it up. When the outdoor air is heated up to 23°C indoors, the absolute amount of water in the air is still the same. But since warmer air can hold more water, the relative humidity goes down to 33%.

On the other hand, warm air can handle more moisture than cooler air. For example, a warm and humid summer with 80% humidity at 30°C, would mean that the outdoor air contained 24 grams/m3 of water. In our homes, 30°C would be very uncomfortable so many would use air conditioners to cool it down again. If you cool it down to below 26°C, the relative humidity level goes to 100% and the water condenses (The dew point). That is why air conditioning systems often have a dehumidifier built-in. Without them, your walls in the home would be soaking wet during the summer.

A 100% relative humidity level would mean that the air is completely saturated with water vapor. Unable to hold any more, it would rain.

HOW TEMPERATURE
AFFECTS INDOOR
HUMIDITY
LEVELS

01Weather

Colder climates often have lower humidity levels than warmer climates as colder air holds less moisture than warm air. In winter, humidity levels tend to be typically lower. Whereas in summer, humidity levels will be higher, as air can hold more water vapor at a higher temperature.

02Everyday actions

Small everyday tasks can affect humidity levels. Cooking, cleaning, dishwashing, breathing, clothes washing, showering, and other indoor processes release moisture into the indoor air, making indoor humidity levels rise.

WHAT CAUSES
CHANGES
IN HUMIDITY LEVELS?

Healthy indoor relative humidity levels are between 30-60%

Mold

21% of the 21.8 million cases of asthma annually are attributable to residential dampness and mold⁴. The humid conditions provide an excellent home for bacteria, as well as mold growth. The excess moisture in buildings can be caused by leaks, rain seeping in through windows and basements, or even rising damp from the ground floors.

Asthma, allergies and respiratory illness

Humidity levels above the recommended 50%, is when the air will start to feel dense and damp. More problems can develop as the levels rise.

Dust mites

Did you know that dust mites could not survive without humidity from the air?⁵ Dust mites like moderate temperatures and high humidity as they absorb water from it, so areas with high humidity levels are great places for them to live. The microscopic creatures can worsen allergies and asthma, so maintaining healthy humidity levels is key to minimizing them and their effects.⁶

Dry skin and eczema

Itching and dryness can be caused by low humidity. Studies have also found that low humidity should be avoided to protect the tear film in your eyes⁷. It can also aggravate certain skin conditions such as eczema⁸. Very dry air can extract moisture from the skin and make eczema worse⁹.

Educational performance

Measurable changes in your ability to concentrate or perform tasks can be caused by even small changes in the relative humidity and temperature.

Influenza

A significant link between low humidity and the easy spread of the influenza virus has been found. One study¹⁰ found that in peak times of low absolute humidity, such as winter when the air is dry, the transmission of the flu increases.

EASY HUMIDITY SOLUTIONS

Simple solutions can help to improve indoor humidity levels in your home. The most important and often the most effective is good ventilation.

In areas of localized high humidity, such as the bathroom and kitchen, use bathroom and range hoods to circulate and extract the air. Opening windows to allow fresh air into your home is also a simple and well-known solution.

By monitoring daily, you can ensure that you achieve the right humidity levels for your home inclusive of common humidity fluctuations and extraneous variables.

WHAT DO MY HUMIDITY
LEVELS MEAN?

Please note, humidity is best considered in relation to temperature. For example, if you have 50% humidity as well as below freezing temperatures outside, you would naturally heat the air up indoors to keep warm. Because of this, condensation can form and you would have a heightened risk of mold formation.

≥70%

Poor high humidity levels. Try making changes such as:

Running a dehumidifier
Open windows for an hour or two on dry days

≥60% and <70%

Fair humidity levels, keep monitoring

≥30% and <60%

Maintain your healthy levels

≥25% and <30%

Fair humidity levels, keep monitoring

<25%

Poor low humidity levels:

Try drying clothes indoors using a drying rack rather than a tumble dryer. Ensure that you have plenty of ventilation when doing so
Decreasing your indoor temperature could help, if possible, but make sure to keep above 15°C
In cold climates, using eye drops and lotion to alleviate itchy eyes and dry skin
Open the door while showering to help spread the humidity from the shower
If you have active ventilation, you can decrease the ventilation at the expense of higher CO₂