Have you noticed bad odors when running your air conditioning system? Maybe your home smells damp, or perhaps it smells stale or musty. Conventional wisdom should lead you to believe that bad odors such as these are not normal. If they occur while running your air conditioning system, dirty sock syndrome could be to blame.

What Is Dirty Sock Syndrome?

Dirty sock syndrome is a phenomenon that’s characterized by bad odors when running an air conditioning system. It’s typically the strongest when you initially turn on your air conditioning system. During those first few minutes, you may notice strong, bad-smelling odors originating from the supply vents.

Depending on the severity of the problem, the bad odors may go away shortly after – or they may linger.  Some cases of dirty sock syndrome can create lingering bad odors that remain for hours. Other and less-severe cases only create temporary bad odors that last for a few minutes. Regardless, dirty sock syndrome refers to the production of bad odors while running an air conditioning system.

Common Causes of Dirty Sock Syndrome

Most cases of dirty sock syndrome involve mold. If there’s mold inside of your ductwork, your air conditioning system may release it. Each time you turn on your air conditioning system, the blower will push the mold-filled air out of the ductwork and into your home’s living spaces.

A dirty evaporator coil can cause dirty sock syndrome as well. Not to be confused with the condenser coil, the evaporator coil is the heat exchanger unit that’s found inside of your home. Air conditioning systems work by blowing air over the evaporator coil. This in turn will remove heat from the air, thereby creating cool air that’s pushed into the ductwork.

If the evaporator coil is dirty, you may notice bad odors while running your air conditioning system. The blower will pick up the dust and debris from the evaporator coil, which will then enter the ductwork before entering your home’s living spaces.

You should check the air filter if you notice bad odors while running your air conditioning system. A dirty air filter is a common cause of dirty sock syndrome. Air must through the air filter before it can be cooled at the evaporator coil. Even if the evaporator coil clean, the air filter might be dirty. With a dirty air filter, contaminants will enter the ductwork that manifests in the form of bad odors.