Stale air smell in the house (What to do about it)

This article discusses the reason and sources of the characteristic stale smell present in houses. We elaborate on the chemical species which cause the stale smell, their sources, and which rooms are prone to it.

What is a stale smell?

Stale smell refers to the characteristic indoor air which is not fresh, due to which the air has an odor, and feels stuffy. This can happen due to the buildup of certain chemicals as well as humidity in the indoor environment.

As a result, the ratio of air contaminants responsible for making the air smell stale to the oxygen levels decreases, making it harder to breathe as well.

Factors that favour formation of stale air

There are a few chemical species as well as biological components that are responsible for making the air seem stale. These include:

  • Water vapour
  • Mold and mildews
  • Tight packed houses
  • Poor ventilation system

Let us discuss these in more detail

Water vapour

In certain areas of the house, such as the kitchen, bathroom, basement, and so on, the humidity levels can be much higher in comparison to the other rooms of the house.

This is primarily due to the presence of water in the vapour form. In higher humidity levels, the air becomes heavier than normal, making it harder to breathe.

Furthermore, water vapour also promotes the growth of microorganisms such as bacteria, mold, and mildew. These microorganisms further contribute to the odour, thereby making the air stale. 

Mold and mildew

Mold and mildew are fungal species that grow favourably under conditions such as presence of organic material, high humidity, low sunlight, and low temperatures.

These conditions are found in certain areas of the house, such as basements, bathrooms, cupboards, air conditioners, and so on.

The spores generated from mold and mildew, alongwith their odor, make the air feel stuffy and produce a stale or musty odor. 

In some cases, these spores can also cause serious health issues, especially in people suffering from a comorbidity, or ailing from respiratory illnesses such as covid.

Tight packed houses

Tight packed houses refers to the modern day construction of houses which utilises windows and doors that pack tightly i.e., have no gaps within.

While this is good in certain conditions, since it prevents the infiltration of outdoor air pollution in the indoor environment, as well as limits the heat exchange rate with the surroundings, especially in the winter season, it also causes poor air exchange rate.

Due to poor air circulation, the amount of free oxygen available starts to decline, while the humidity levels as well as the concentration of pollutants responsible for the stale air smell start to rise.

This effect is more pronounced especially in winters and monsoons, when the relative humidity levels are high and the temperatures are comparatively lower than the other seasons.

Poor ventilation system

Ventilation is an important feature in every house. Apart from the fact that adequate ventilation keeps the air fresh and prevents stale air smell, it also removes the indoor air pollutants by bringing in fresh outdoor air, while carrying the indoor air away.

However, some places lack adequate ventilation, which can happen due to various reasons. In such cases, the indoor air pollution keeps aggregating, and growth of mold and mildew can also take place.

A common example of this is seen in basements which typically do not have a natural source of ventilation. Articles such as clothes, furniture, and walls are more prone to mold and mildew than the other rooms of a  house.

Potential sources of stale air

Given the conditions that favour the increase in the humidity levels, as well as the formation of microorganism volatile organic compounds (MVOCs), there are certain potential sources of stale air, which include:

  • Bathrooms
  • Basements
  • Air conditioners

Let us discuss these in more detail.


Bathrooms are the areas where a lot of water is utilised, for cleaning and bathing purposes. Such processes give rise to high levels of humidity.

Furthermore, in some cases, the laundry baskets are stored in bathrooms as well. Due to the accumulation of moisture in the room, as well as the availability of an organic source of nutrition i.e., clothes, there are higher chances of development of mold.

This in turn leads to the higher production of mold spores in the bathroom, which in turn gives rise to the stale air smell in the bathroom.


Basements are rooms that are present beneath the ground level. Therefore, with respect to other rooms, basements have lesser sources of natural ventilation.

Furthermore, basements are also prone to seepage issues, given the fact that they are below ground level. Lastly, basements are typically used as a storage room for items such as clothes, furniture, books and newspapers, and so on.

All these factors collectively create the microclimate that is best suited for rise in humidity levels, as well as the growth of mold on favourable surfaces.

Therefore, basements are prone to develop a stale air smell, given the environment it creates, as well as the lack of ventilation.

Air conditioners

Although air conditioners are highly regarded for maintaining the optimal temperatures in a room, they are also known for their ability to cause the stale odor of the indoor air.

This is because air conditioners keep circulating the same air within a room, which causes a rise in the levels of pollutants in the room.

Furthermore, since they keep a cool environment, they also promote growth of mold spores, especially within its components, as in some components such as the evaporator coil, the dark and humid conditions required for mold growth prevail.

Therefore, while the air conditioner keeps the room cool, it can also cause as well as exacerbate the stale air smell within the room.

This is especially observed in older air conditioning units or units that haven’t been maintained properly.

How to prevent stale air smell

There are multiple ways in order to minimise as well as prevent the buildup of stale air smell within a room. Some of these are:

  • Opening windows and doors
  • Installation and regular maintenance of HVAC systems
  • Regularly cleaning your house
  • Investing in an air dehumidifier
  • Using an air purifier

Let us discuss these in more detail.

Opening doors and windows

Opening your doors and windows for some time during the day helps to increase the air exchange rate with the outdoor air. As mentioned earlier, this helps to remove the indoor pollutants as well as the odor, while introducing fresh air.

However, it is important to check the outdoor pollen and mold count, since on days of high concentration levels, the smell will get further exacerbated.

Installation and regular maintenance of HVAC systems

HVAC refers to Heating, Ventilation, and Air Conditioning. Although in some places it is already present, it might be the case that certain places may not have it.

HVAC systems are especially helpful for places which do not have proper sources of natural ventilation, such as basements. They help to regulate the room conditions in a manner that prevents growth of mold.

However, one should also ensure that the HVAC systems are being maintained on a regular basis, since faulty systems as well as older units may sometimes contribute to the stale air smell.

Regularly cleaning your house

It is important to keep your house clean, especially surfaces such as beddings, carpets, or places where people usually are present.

Studies have shown that nearly 60% of total dust accumulated in the indoor air originates from outdoors. Within these dust particles, mold spores and other substances can be present, which cause indoor stale odor.

By regularly dusting surfaces and cleaning the house, there are lesser chances of accumulation of substances that give rise to stale air smell.

Invest in an air dehumidifier

As seen from above, high humidity levels play a major role in the generation of stale air smell indoors. Therefore, it is important to regulate the indoor moisture levels.

This is where air dehumidifiers come in the pictures. These devices, as the name suggests, lower the humidity of the indoor environment, therefore keeping the air dry and hampering the growth of mold.

Use an air purifier

Air purifiers are devices that help to keep the air in an indoor environment clean. They not only remove pollutants that give rise to stale air smell, but can also remove the smell efficiently.

HEPA filters with an activated carbon filter as well as a germicidal UV light chamber are the best option for getting rid of the stale air smell in a relatively short amount of time.

Other FAQs about Air Quality that you may be interested in.

Can a dusty house make you sick?

Stale air symptoms

Why is my room stuffy in the morning?


Stale air smell can be caused due to reasons such as high humidity levels in the house, which give rise to mold and mildew, and other factors as well.

Therefore, in order to prevent and minimise this, it is important to improve ventilation, as well as use an air dehumidifier and an air purifier.


Do air fresheners and essential oils help to get rid of bad smells in the house?

Yes, air fresheners and essential oils can help to get rid of bad smells in the house. However, this is only a temporary solution, since once the effect of these fragrance compounds fades away, the sources of odors are still persistent, thereby causing the bad smells to occur once again.

As a solution, it would be ideal to rather identify the sources of unpleasant odors in your house and take care of them, as this is a viable solution that would last for a longer time.

Can appliances that regulate physical parameters of the air cause stale smell in the house?

Yes, appliances that regulate physical parameters of the air can cause stale smell in the house. This can be seen particularly in appliances such as air conditioners as well as HVAC (Heating, Ventilation, Air Conditioning) systems.

If the filters are old, chances are that they are overloaded with pre-existing dust deposits. This causes a decrease in the air inflow rate for the device, due to which the air circulation gets impeded.

Furthermore, these devices can also develop dark and humid conditions, which help mold and bacteria to thrive. Therefore, these appliances may end up exacerbating the indoor air quality and will give rise to the unpleasant odor as well.

Why does my house smell like gas but no leak?

This can happen due to the presence of sulfur in the indoor ambient air. Sulfur, like gas, has a characteristic rotten egg smell. This can emanate from sewage or from organic discards as well.

However, it is not necessary that it will always be the case. Gas leaks are hard to spot, and even if it isn’t in your house, there might be chances that there is a leak in your neighbouring house.

In such a case, open all doors and windows, and contact a professional who can help better.


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