No, nobody has secretly been stuffing unwashed socks into your ventilation system (unless you know something we don’t). This unpleasant odor coming from the vents when the air conditioner turns on is a common problem known, appropriately, as “dirty sock syndrome.” You want to have it fixed, not just to eliminate the sour odor from wafting around your house, but because it indicates a problem with the air conditioning system that will impair its performance and cost you more to run it.

Follow us below as we look more into dirty sock syndrome.

The Source of the Odor

Although you aren’t literally smelling dirty socks, this odor comes from the exact same source that causes dirty socks to smell—bacteria. As bacteria feeds on chemicals, it releases a compound with a foul smell. Different types of bacteria release different odors, such as the bacteria involved in brewing or cheese-making. The specific bacteria odor you’re detecting from the ventilation system is due to the growth of bacteria along the evaporator coil of the air conditioner.

The evaporator coil is the spot in the AC system that does the actual cooling of the air. Warm air moves past this coil on its way to the supply ducts. As the warm air contacts the coil, the cold refrigerant in the coil absorbs heat from the air and cools it. It also causes the moisture in the air to condense along the surface of the coil. This creates a damp environment that attracts organic growths like mold and mildew, both of which contain the bacteria that creates the dirty sock smell. Because all the air in the ventilation system must pass over this coil, the odor will spread throughout the house.

The Consequences

The bad odors are only the beginning of the trouble. When any grime, mold, or mildew forms on the evaporator coil, it restricts the coil’s ability to absorb heat. An AC will suffer from a drop in energy efficiency because of this. Worse, it can lead to the coil freezing because the refrigerant inside will remain too cold. This will eventually lead to the AC providing no cooling at all.


When dirty sock syndrome strikes, you’ll need to call for professional AC repair in North Potomac, MD to correct it. However, you can take future steps to help prevent it. The most important is to always have your AC maintained in spring before the summer arrives. A frequent cause of mold and mildew growth in an AC is poor condensate drainage causing the moisture level inside the air conditioner to rise. Maintenance will clean the condensate system to make sure it works at its best. Maintenance also cleans the coils, which makes it less likely that mold and mildew will grow on it.

Another prevention tool is to replace an aging AC. Seems extreme, but if your air conditioner is older than 12 years and develops dirty sock syndrome despite regular maintenance, it often signals the system is in its final decline.

Call us for help with your “dirty sock syndrome” air conditioner. At Tuckers Air Conditioning, Heating & Plumbing, we pledge to exceed expectations at every turn!