red sock with blue stripes representing dirty sock syndrome for air conditioners

Mention dirty sock syndrome to any HVAC professional, and they’ll understand what you’re saying. To the rest of us, dirty sock syndrome sounds like a laundry issue rather than an HVAC issue. Dirty sock syndrome refers to the musty smell air conditioning systems sometimes emit when turned on. This moldy, mildew-like odor most often occurs during springtime. Dirty sock syndrome has specific causes; luckily, there are several DIY solutions to eliminate the stinky smell.

What Causes Dirty Sock Syndrome?

The dirty sock smell is actually the odor of mold and bacteria. Dirty sock syndrome occurs when moisture, dust, and dirt accumulate on the air conditioner’s evaporator coils and foster mold and bacteria growth. Clogged drain pans can also be sources of mold and bacteria growth.

Dirty sock syndrome usually occurs in springtime when air conditioners are infrequently used, and the length between cooling cycles is longer. Moisture, duct, and dirt build up during the long intervals of inactivity.

dust, dirt, bacteria on air conditioner evaporator coil

How to Fix Dirty Sock Syndrome

In many cases, homeowners can take steps to eliminate dirty sock syndrome and prevent it from returning. If performing maintenance tasks yourself is not an option, call a professional HVAC service.

To eliminate and prevent dirty sock syndrome:

  • Replace your filter
  • Clean your evaporator drain pan
  • Clean your ductwork
  • Clean your evaporator coil
  • Invest in a dehumidifier
  • Utilize UV technology

Replace Your Filter

Your air filter traps contaminants in your home’s air. Dust, dirt, pet hair, pollen, and dead skin cells build up in the filter over time and impede airflow around and inside your air conditioning unit. As a result, the moisture your air conditioner removes from your home’s air fails to evaporate. The air filter becomes damp, and mold spores, and bacteria begin to grow.

A simple solution is to remove the air filter and replace it with a new one. You may see mold spores or notice a musty smell coming from the old one. The dirty sock smell might improve within hours of replacing the filter. How often to change an air filter depends on various factors. Continue to change the filter regularly, every 30-90 days depending on the type and quality.

Clean Your Evaporator Drain Pan

Your evaporator drain pan collects condensation that drips from the evaporator coils. When dirt accumulates in the pan or the pan’s drain hole becomes clogged, mold and bacteria often begin to grow in it. A full pan of water indicates a clogged drain pan or drain line.

The primary pan can usually be removed and cleaned with hot water. A paper clip or piece of wire can be used to clear blockages from the drain hole. If you’re not up to the task, hire an HVAC professional to perform maintenance.

Clean Your Ductwork

Bacteria and mold can grow in your home’s ductwork, especially in the duct’s tight spaces, like joints and corners. Possible causes include a dirty filter impeding airflow, warm air leaking into the ducts through gaps, keeping the inside temperature too low, or possessing an air conditioner that is too large for the size of your house.

Your best bet is to hire a professional duct cleaning service to ensure the job is done thoroughly. Mold will reappear if the ducts are not cleaned completely or if the mold is not entirely removed.

Clean Your Evaporator Coil

The evaporator coil is responsible for cooling your air. Condensation is created when the house’s warm air comes in contact with the coil’s cold, refrigerant-filled copper lines. Dirt and dust accumulate on the coil over time and reduce evaporation of the condensation. Mold begins to grow on the wet coils and causes a stench.

Cleaning the evaporator coil eliminates the odor. To clean the coils, switch off the power to the air conditioning unit and open the access panel of the indoor air handler unit. Following the manufacturer's directions, the coils can be blown clean with compressed air and washed with a no-rinse evaporator coil cleaner. Your other option is to hire a professional to clean the coil.

Invest in a Dehumidifier

A dehumidifier won’t eliminate dirty sock syndrome, but it can prevent it from recurring since moisture is the initial cause of it. A whole-house dehumidifier or a portable unit in the basement will remove excess moisture from the air.

Utilize UV Technology

Once again, an air purifier utilizing ultraviolet (UV) light isn’t a solution to dirty sock syndrome but can prevent a recurrence. The odor reminiscent of dirty socks is the odor of mold and bacteria. UV light kills mold and bacteria. Since air conditioners are typically installed in dark spaces like basements and attics, they don’t get much UV light from the sun and can be breeding grounds for mold and bacteria. Air purifiers with UV technology are a great solution.

Can Dirty Sock Syndrome Make You Sick?

Dirty sock syndrome can negatively affect your health. The odor you smell results from mold and bacteria growing on parts of your air conditioner. Air that passes over moldy evaporator coils or through moldy ducts is blown into every room of your house, including bedrooms.

Mold exposure may cause flu-like symptoms, allergies, respiratory illnesses, and fatigue. According to a Mayo Clinic study, mold is the cause of most chronic sinus infections. Family members sensitive to mold, have allergies, or asthma may experience increased symptoms.

Symptoms of mold exposure may include:

  • Coughing
  • Wheezing
  • Itchy skin
  • Skin rashes
  • Nasal drip
  • Watery and red eyes
  • Headaches
  • Fatigue
African American woman with sick from dirty sick syndrome blowing her nose at home.

Will the Musty Smell Go Away on Its Own?

The musty smell may diminish after initially turning on the air conditioner at the beginning of the cooling season. However, the dust, dirt, mold, and bacteria that caused the smell will remain. The problem must be addressed to ensure good air quality in your home.

Eliminate Dirty Sock Syndrome for Good

Dirty sock syndrome is a stinky problem with definitive causes and simple solutions. Eliminating the excess moisture produced by your air conditioner and removing dirt and mold within your air conditioning system are essential.

Before you call a professional, try these DIY solutions:

  • Replace your filter
  • Clean your evaporator drain pan
  • Clean your ductwork
  • Clean your evaporator coil

Call a professional if:

  • DIY solutions are not an option for you
  • DIY solutions don’t resolve the problem
  • There is mold in your ductwork
  • Your air conditioner is not cooling properly

Prevent dirty sock syndrome by:

  • Changing your air filter regularly
  • Invest in a dehumidifier
  • Invest in an air purifier with UV technology
Air conditioning

1 comment

Jim Scanlon

Jim Scanlon

realistically, the only solution to the problem is replacing the coil with a coated coil. all the other smoke and mirrors that everyone else throws out may temporarily “Band-Aid” the problem but it is not a long term solution. in most cases the problem only occurs during heating season and only when the unit goes into defrost mode. it began when manufacturers started producing coils with aluminum. and it goes without saying…this only pertains to heat pump units. if it happens in a gas fired unit…it isnt dirty sock syndrome (as we know it). its another issue. also…it is environmental from the standpoint of where the air handler is installed. an inside (in the home) air handler is less likely to have the issue whereas an air handler installed in a crawl space is more likely.

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