Key Takeaways

  • Air conditioning units keep you cool and remove particles from indoor air, but running your AC with a dirty filter can lead to upper respiratory symptoms.
  • It is important to routinely clean your AC unit to keep it free from mold and dust.
  • Going from a high temperature outside to a cold temperature inside can exacerbate respiratory symptoms for people with asthma and COPD.

As we head into summer in tandem with unpredictable air quality from wildfires, air conditioning is an important tool both to keep cool and and to filter out air pollutants. However, you may not realize that unclean or poorly managed air conditioning units can affect your health by causing dry skin, allergy and asthma symptoms, and even illness.

“Most people in industrialized countries spend up to 90% of their time indoors, so it is important to recognize the health risks of indoor exposures and pollutants,” Lauren Eggert, MD, clinical assistant professor of pulmonology, allergy, and critical care medicine at Stanford Health Care, told Verywell via email. “In general, the health risks from exposure to air conditioning are low and more so associated with improperly-maintained air conditioning units.”

Portable and fixed in-duct heating, ventilation, and air conditioning (AC and HVAC) units are great for eliminating pollutants from outside air and recirculating inside air, but filters need to be cleaned on a routine basis to keep dangerous small particles (viruses, bacteria, mold, and allergens) out of your lungs. Here’s how unclean air conditioners can make you sick and how to prevent it from happening to you.

How a Dirty AC Can Make You Sick

Some of the potential health risk of air conditioning are specifically tied to the quality and cleanliness of its filters and ducts.

“Dirty air conditioning filters may be contaminated with mold, fungus or other microorganisms,” a representative for the California Department of Public Health told Verywell. “This may lead some occupants, especially if sensitive to molds, to have breathing problems.”

HVAC units are designed to filter air pollutants and contaminants from indoor air circulation. However, if filters are not cleaned or replaced according to manufacturer recommendations, they can become magnets for air particles and microorganisms that can trigger asthma, allergies, and other respiratory symptoms. 

Studies have found that using a whole house filter (WHF) with a disposable high-efficiency MERV 12 (Minimum Efficiency Report Value) filter is effective at removing small particles that can trigger asthma attacks. However, filters can be a reservoir for asthma triggers if they are not maintained properly. 

Mold Growth

Mold is another dangerous health hazard that can grow and contaminate air conditioner ducts and filters if they’re not routinely cleaned. Indoor moisture and high humidity are the perfect conditions for mold spores to grow and circulate through your home.

Breathing in mold spores can lead to a number upper respiratory symptoms, including:

  • Stuffy nose
  • Wheezing
  • Breathing difficulty
  • Fever
  • Cough

People with asthma, and those who are allergic to mold are at an increased risk of illness from indoor mold exposure.

There is not a specific test for mold exposure. A doctor or allergist will usually conduct an allergy test to determine a mold allergy.

Spread of Airborne Illness

Air conditioners can circulate dangerous particles and contaminants if they have dirty air filters or have a filter that is not designed to remove infectious viruses, bacteria, or air pollutants.

Studies have shown that having a high-efficiency particulate air (HEPA) filter is essential to prevent illness, including the SARS-CoV-2 virus that causes COVID-19. 

Legionnaires’ disease, a type of pneumonia caused by the bacteria Legionella pneumophila, is the most talked about illness that can spread through contaminated water from an air conditioning system. 

According to the American Lung Association (ALA), there are about 20 Legionnaires’ outbreaks a year affecting about 5,000 people. Most outbreaks occur at hotels, long-term care facilities, and hospitals.

Temperature-Related Health Concerns

Even if an air conditioner is clean and working properly, some groups may be more sensitive to the way it alters the air.

Low Humidity

Your skin is vulnerable to the circulation of air conditioning. The function of an AC unit is to cool the space down by removing heat and lowering humidity, which can dry out skin and exacerbate skin conditions such as atopic dermatitis (eczema) and senile xerosis (rough, dry, itchy skin).

“Air conditioning pulls water out of the air, creating a lower humidity environment which can cause or worsen dry skin,” Megan Poynot Couvillion, MD, a board-certified dermatologist in Houston, told Verywell via email. “When our skin is dry, the barrier that seals in the moisture has been disrupted, and needs to be restored.”

A gentle, fragrance-free cream or ointment can help lock in your skin’s moisture.

Fluctuations in Temperature 

Moving from a hot outdoor environment to a cold, air-conditioned indoor environment can have a negative impact on your respiratory tract, especially if you have chronic lung conditions such as asthma and chronic obstructive pulmonary disease (COPD).

One study demonstrated that exposure to a sudden decrease of 5 degrees can lead to an exacerbation of respiratory symptoms.

Tips for Maintaining Your Air Conditioner 

As long as you properly maintain your AC system, there is little chance that you could become sick from spending long periods of time in air conditioned spaces.

Here are some helpful tips on how to properly maintain your AC cooling system:

  • Change your air filter every three months or according to manufacturer recommendations.
  • Use HEPA filters which are effective at removing dangerous air particles.
  • Make sure windows and doors are closed when running your AC unit.
  • Run AC on recirculate.

“People should keep their windows closed and run an air conditioner, but make sure the fresh air intake is closed and the filter is clean,” Eggert said. “This helps circulate the air and keep it clean. Air conditioners in hot and humid climates also help keep humidity levels down which prevents the growth of mold and other things which can affect lung health.”

What This Means For You

As we become more reliant on air conditioned spaces to avoid heat stroke and air pollution caused from climate change and global warming, it is important that we stay on top of routinely changing out filters and cleaning AC units in order to avoid respiratory issues, infections, and general irritation.

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