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Dirty Sock Syndrome (The Bad Smell Coming from an AC System)


If you have a terrible smell coming from your HVAC system, you may have dirty sock syndrome.

But what is dirty sock syndrome, and what causes it?

We will cover that in this guide, including how to remove and prevent dirty sock syndrome from making your home smelly and negatively impacting your IAQ.

Jump to Section

  1. What is dirty sock syndrome?

  2. What causes dirty sock syndrome?

  3. How to get rid of dirty sock syndrome?

  4. How to prevent dirty sock syndrome?

  5. Conclusion

What is dirty sock syndrome?

Dirty sock syndrome is the term used to describe the bad smell that may come from your AC or HVAC system.

The smell comes from mold and bacterial growth that gets built up on your AC coils over time.

Asides from the smell, dirty sock syndrome can actually be harmful to your health.

What causes dirty sock syndrome?

Since dirty sock syndrome comes from the mold and bacterial build-up on your coils, the better question is what causes the mold and bacterial build-up?

Mold and bacteria grow best in moist, humid environments; the ac coil produces condensation and is a great breeding ground for mold and bacteria to grow.

Any bacteria that makes its way to the coil through the ventilation system can stick to the coils and allow it to grow.

Often, the build-up is out of control, which can block the airflow through the coil, causing high static pressure, which is also not good for the longevity of your HVAC system. And can lead to AC capacitor failures as well.

How to get rid of dirty sock syndrome?

The only way to get rid of dirty sock syndrome is by removing any mold or bacteria growth from the coils.

To do so, you will need to clean the evaporator coils in your HVAC system.

You can attempt to clean it yourself; however, we recommend contacting your local HVAC professional as they have the proper knowledge, equipment, and cleaning supplies.

Cleaning the coils will remove the mold and bacterial growth from the coils and remove the smell as well.

In rare cases, if you live in humid areas, the build-up can happen in your ducting as well. If that is the case, you will need to replace your ductwork.

Duct cleaning will not remove bacterial growth from your ducting. Duct cleaning removes dust and debris from the ductwork, not mold or bacteria.

There are antimicrobial ducts, which are made of a material that prohibits mold and bacterial growth.

You can ask your local HVAC professional if they have and install antimicrobial ducting.

How to prevent dirty sock syndrome?

There are a few ways you can prevent dirty sock syndrome.

The most effective is installing a UV purifier near your evaporator coils.

The UV rays kill mold and bacteria, therefore not allowing them to grow and cause a bad smell.

Just be sure you choose a UV purifier that doesn’t produce ozone. Ozone can cause irritation in your lungs and increase allergies.

The second way to prevent dirty sock syndrome is by controlling the humidity in your home.

Bacteria grow best in moist, humid environments; you want to be sure your home is not too humid and isn’t a prime breeding ground for the bacteria to grow.

The optimal humidity in a home is between 30-50%. Therefore we still would recommend UV light over a humidity control system as it is active in killing bacteria.

Nonetheless, both a humidity control system along with a UV light/purifier would be the best protection from dirty sock syndrome.


Dirty sock syndrome causes a bad smell in your home and is not healthy for you due to the nature of the cause of it (mold/bacteria).

The only way to remove dirty sock syndrome is by removing the mold and bacteria built up within your HVAC system.

If the build-up is on the coils, you can get your evaporator coil cleaned. And if it is within your ducting, unfortunately, you will need to get them replaced.

In rare cases, the build-up will be too much, to the point where you will need to get a new coil.

To prevent dirty sock syndrome, you can install a UV light near the coil. This will kill any mold and bacteria, preventing them from growing.

You also want to ensure your home is not too humid, allowing for a good environment for the mold and bacteria to grow.

If you think you have dirty sock syndrome in your home, then contact an HVAC professional.

They will check your coils and ducting for any mold and bacterial growth and can help you with cleaning them.

If you have any questions regarding dirty sock syndrome or HVAC, contact us. We are here to help.

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