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It may be difficult to describe the specific odor that you associate with “stale air,” but you definitely know it when you smell it. Whether you encounter it in a crowded room or a damp basement, stale, stuffy air is unpleasant, but is it also bad for your health? With a rise in energy-efficient homes and buildings—and an increasing public awareness about the importance of indoor air quality—more and more people are starting to wonder whether stale air is just a minor annoyance or a legitimate cause for concern. Below, we will explore what causes stale air and whether it can impact your health.

What is stale air?

Stale air is no longer fresh and can have an unpleasant smell. When indoor air starts to smell stale or feel stuffy, it is usually due to a buildup of certain chemicals as well as humidity in the air. The ratio of airborne contaminants to oxygen starts to increase because of a lack of fresh air. . These contaminants are mostly biological byproducts, such as exhaled carbon dioxide, and microbial volatile organic compounds (MVOCs).

MVOCs are carbon-based molecules with a very low odor threshold, meaning even the smallest microbial colonies can start to cause a room to smell. These MVOCs are caused by the growth of bacteria and fungi and are responsible for the strong, distinct musty odors that we associate with certain rooms, such as locker rooms. Bacteria and fungi can create ammonia, sulfurous compounds, and a broad range of other VOC metabolic waste products that can affect the smell of a room. These metabolic waste products are present in any part of a building with consistent moisture (such as toilets and drains) and, without proper ventilation, they can start to cause the air in a room to feel stale.

As far as biological byproducts, if you start to notice a stale, musty smell in a crowded room, it is probably because of the temporary increase in humidity and carbon dioxide caused by people breathing. Our exhaled breath has a high moisture content that can accumulate to raise the relative humidity in an enclosed room.

Is stale air bad for you?

When you learn about the buildup of carbon dioxide, humidity and MVOCs that can create stale, stuffy air, you may start to worry about how exposure to this air can impact your health. Fortunately, the accumulation of bad smells and humidity is not necessarily bad for you, especially when you are not consistently exposed to it. However, the lack of fresh air in a room means a buildup of harmful pollutants can occur. It is this buildup that should be cause for concern, as it indicates a poor indoor air quality situation. Some studies have linked chronic MVOC exposure to eye, nose and throat irritation, coughing, wheezing, fatigue, headaches and other symptoms typically associated with sick building syndrome.

Excess carbon dioxide in the air is usually temporary and should start to clear out of an enclosed room when the number of people in the room decreases. If you are in a building, such as a school or an office, with consistently high carbon dioxide levels, you may notice a general sense that the air is stuffy or stale, sometimes accompanied by drowsiness or fatigue. After all, one of the purposes of breathing is to remove carbon dioxide from your body. If the carbon dioxide levels in your blood get too high, you may experience rapid breathing and confusion.

Overall, occasional exposure to stale air should not be a source of concern. However, for rooms that have consistently stale air, the humidity and buildup of MVOCs could lead to more severe indoor air quality issues, including mold growth.

What causes stale air?

Stale air, at its root, is caused by a lack of ventilation. When air is confined to an enclosed room, pollutants, moisture and carbon dioxide can start to accumulate. You may notice your house may feel stale and stuffy after an extended vacation in which your windows and doors remained mostly shut, especially if you had your HVAC system turned off or down. You may also notice an increase of stale air in the winter months when we take additional care to stay indoors and seal our homes from the cold outside. However, you probably will probably not experience humidity increases in the dry winter months.

According to the EPA, in the past, buildings had high air exchange rates, meaning that new air was brought into the building, old air was filtered out, and any airborne pollutants were diluted with fresh air intake. Unfortunately, this air exchange uses a lot of energy when the air outside is a different temperature than the indoor air. Modern, energy-efficient buildings are designed to prevent unwanted airflow in and out of a house, increasing your chances of encountering stale and stuffy air. Airtight windows and doors are great for the electricity bill, but they may take a toll on your indoor air quality if you do not take measures to increase the ventilation in your home.

When you notice stale air, you are smelling small amounts of airborne contaminants. On their own, pollutants at this level are not enough to worry about, but when they start to add up, the air quality can suffer. When the air in a room is continuously recirculated, instead of being filtered out with outside air, carbon dioxide and pollutants in the air can start to accumulate to potentially harmful levels. This can also be a problem when the HVAC system is not designed to ventilate a room with an increased number of people. This brings up the question: is there a way to prevent or remove stale, stuffy air without putting a strain on your wallet?

diagram of how to reduce stale air in home

How can you get rid of and prevent stale air?

There are a number of steps that you can take to prevent stale air in your home, school or office without causing a considerable increase in your monthly energy bill. The main thing that you should think about is increasing the ventilation in the affected rooms. Your HVAC system, when working properly, should filter out stale air and replace it with fresh air. This will help dilute any humidity or MVOCs causing your room to feel stuffy. You can also increase a room’s ventilation by:

  • Installing a window fan in the room. Some window fans have settings to pull stale air outdoors. Make sure to follow the manufacturer’s instructions to ensure efficient ventilation.
  • Using exhaust fans in your kitchen, bathrooms and laundry room. Exhaust fans help get rid of stale, humid air. This is especially important in any enclosed rooms in which moisture tends to build up.
  • Changing your HVAC filter regularly. A dirty or clogged HVAC filter will decrease the efficiency and effectiveness of your ventilation system. Additionally, if mold or bacteria has started growing on your filter, your heating and air system could be blowing these pollutants back into your home. If you have not already, consider switching to a HEPA filter to further reduce the levels of airborne pollutants in your indoor air.
  • Opening your windows. If the outside weather allows (and the pollen and mold spore counts are low) opening your windows can be a great way to introduce fresh air into your home.
  • Using an air purifier. An air purifier can help provide fresh, clean air to your home. Many traditional air filters can only capture particles, which would not be helpful with unpleasant smells. The Molekule PECO technology can destroy airborne chemicals, including those that make up odors.

In addition to increasing the ventilation in your home, decreasing your relative humidity can also help get rid of stale, stuffy air. A dehumidifier can keep your home’s relative humidity at a level that can help prevent mold growth and stale air, as well as relieve some allergy and asthma symptoms.

While stale air generally is not a cause for concern, it can still be unpleasant, and cause greater air quality issues if left unattended. You cannot always avoid encounters with stale air, but you do not have to settle for stuffy air in your home or office. By increasing a room’s ventilation and decreasing the room’s humidity, you should be able to get rid of any stale air problems you may experience.

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