Why Humidity and Cold Air Trigger Asthma

by John Bottrell Health Professional

Every asthmatic should be aware that both humidity and cold air are two very common asthma triggers. So why is this? What can you do about it?

It's been common wisdom for years that a cool mist humidifier helps with croup, inflammation and narrowing of a child’s airways. Put a croupy kid in the hot and steamy bathroom and the swelling gets better.

Another method that often works for croup is taking the child outside in the cold winter air. This is why many times when a parent decides to take the child to the hospital, in the dead of winter, the child is fine by the time they arrive in the emergency room.

This is true for croup, so it was also theorized in past decades that it must also be true for asthma attacks. Most doctors are aware of this fallacy. In fact, doctors recognize that both cold air and humidity can actually trigger an asthma attack.

When I was little boy way back in the 1970s, my pediatrician recommended my parents have me sit in the hot steamy bathroom when I was having trouble breathing. It was also recommended I have a humidifier in my room.

Both of these made my asthma worse, not better. Yet I was a kid, so how was I to tell my parents that? My doctor and parents thought they were doing something good, yet their wisdom was flawed (based on what we now know about asthma and triggers).

I wrote a post before how low and high humidity can trigger asthma. Studies show that a humidity of 50 percent or greater may lead to a greater incidence of asthma trouble.

Two common theories for this are:

  • Humid air is heavier and harder to breathe

  • Humid air harbors fungus, molds and dust mites that trigger asthma

Humid air is most often a problem in the summer months, especially in August and September.

(On a side note here, when I was a kid there was also a fear that air conditioners were bad for asthma. That was a fallacy that led to many uncomfortable August car rides.)

As I wrote before, I also remember having asthma trouble when my brothers and I would go sledding. I'd usually have to quit early and arduously walk home with my asthma symptoms raging.

Now we have research that shows air that is too dry can also trigger asthma. Air tends to be drier in the winter months. The reason is that the colder the air, the less water it can hold.

When you inhale cold, dry air, it can dry the mucus membranes lining your lungs, which are your body's natural defense mechanisms against viruses and bacteria. If you have asthma, these weather conditions can also lead to increased infections. And we know viral infections are a common asthma trigger.

Dry mucus membranes can also aggravate allergy symptoms. And considering 75 percent of asthmatics have allergies, this is important as well when considering temperature and air quality as triggers.

Now that you understand dry air can trigger asthma, consider the following:

Exercise can trigger asthma

Rapidly breathing in air dries inspired air as it moves through the upper airways, which ultimately dries the airway, which then releases histamine that can increase inflammation of the air passages in your lungs. This then leads to bronchospasm. The fact runners tend to breathe through their mouths only exacerbates this problem because the nose is a better humidifier than the mouth.

Mouth breathing can trigger asthma

Your nose humidifies inspired air, so if you breathe through your mouth, this air is not getting sufficiently humidified. This is especially important during the winter months when the air is drier. Studies have linked nasal congestion with severe asthma, and I think this is one of the main reasons -- those with sinus trouble typically breathe through their mouths.

Cold air triggers asthma

Again, this is true because the colder the air, the less humid the air is. This is why asthmatics, especially those with exercise-induced asthma, have trouble exercising outside when the air is cold. Rapid breathing of cold, dry air triggers asthma.

To prevent asthma, the Centers for Disease Control and Prevention recommends humidity be set between 35 and 50 percent. Humidifiers can be used in the winter months, and air conditioners and dehumidifiers in the summer months.

It's good wisdom to know that cold air, dry air, and humid air can trigger asthma. It's also important to know that by working with your doctor to control your asthma, you should still be able to continue doing the things you love most. A personalized approach to your daily habits and exercise preferences can allow you to live life to the fullest, while minimizing asthma attacks.

John Bottrell
Meet Our Writer
John Bottrell

John Bottrell is a registered Respiratory Therapist. He wrote for HealthCentral as a health professional for Asthma and Chronic Obstructive Pulmonary Disease (COPD).