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Dirty Sock Syndrome - What It Is and What to Do

Where is that awful smell coming from? You’ve kept the house clean, the clothes hampers are all empty, and you’ve taken out the trash. Heck, you’ve even cleaned the cat’s litter box and washed the dog. Still, your house smells like a poorly ventilated locker room.

Think for a minute. Does the smell occur when your HVAC system switches on? If that’s the case, you’re experiencing Dirty Sock Syndrome (DSS).


In a word, bacteria. The particular bacteria causing the foul locker-room odor in your home grows on the coils of your air conditioner or heat pump when some particular conditions occur. Particularly in the spring and fall your system may cycle back and forth between heating and cooling modes. This combination of heating and cooling can cause excess moisture to accumulate on the coils of the unit, which encourages bacterial growth and mold. Once mold and bacteria have grown on the coils, you’ll experience the foul odor of DSS every time your system turns on and air passes over the coils to cool your home.

While DSS is usually the cause of foul odors coming from your HVAC system, it’s important to rule out some other causes. If you experience the odor all the time or when the heat is on, be sure to rule out these potential causes of odors in your home.

  • Dirty drip pans or pans with standing water.
  • Clogged or incorrectly connected drain lines.
  • Dead animals near ductwork or living areas.
  • Old and leaking ductwork.


Given the right conditions, Dirty Sock Syndrome can occur in almost any home. But some circumstances make it more likely.

Homes with gas furnaces are less likely to experience DSS because the high heat output of a gas furnace can kill off the bacteria causing DSS. Conversely, systems with electric furnaces and standalone air conditioners are at more risk of experiencing this odorous condition.


For most people, Dirty Sock Syndrome is an annoyance but doesn’t present any danger. Having said that, the circulation of mold spores and bacteria around your home by your HVAC system can cause complications for many. In particular danger of being affected by mold and bacteria are:

  • Persons with compromised immune systems.
  • Those with respiratory conditions like asthma.
  • The very young and the elderly.
  • People suffering from allergies.

Here’s the bottom line. It’s hard to predict who may be adversely affected by Dirty Sock Syndrome. If your home is experiencing this problem, you should take concrete steps to address the underlying problem and eliminate the mold and bacteria that cause it.


Fortunately, Dirty Sock Syndrome can usually be addressed and fixed rather easily. Since the source of the odor is mold and bacterial growth, a good cleaning of the coils of your air conditioner will usually take care of the problem.

But before you start power-washing your heat pump, understand that this is a job that should be left to professionals. They’ll need to cut the power to your unit and access the interior to inspect and clean the components that are involved. And while they’re doing that, they’ll be able to inspect your unit to ensure there are no other problems that may need to be addressed.

In some severe cases, the evaporator coils for your air conditioner may need to be replaced. While this is certainly more expensive, it may be covered by the warranty on your unit, so check your paperwork, or with the contractors who installed the unit.


As the old saying goes, “A stitch in time saves nine.” By performing some simple preventative measures you can reduce the chances of experiencing DSS in your home.

  • Replace your filters regularly. High-quality filters can help trap and eliminate bacteria and mold before it becomes a problem. Change more frequently if you keep pets in your home.
  • Have your ducts cleaned professionally.
  • Most importantly, have your HVAC system serviced regularly.

Regular maintenance and service will provide the best protection against your HVAC system developing Dirty Sock Syndrome, as well as ensuring that your system operates at the peak of efficiency all year round..

If your system isn’t checked regularly, consider a Membership with us. Our membership plans save you money on regular maintenance and servicing, plus provide you with peace of mind.

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3 comments on “Dirty Sock Syndrome - What It Is and What to Do”

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