If you have asthma, it may be harder to breathe humid air. That’s because asthma causes your airways to constrict, and humid air contains more moisture making it thicker.

For most of us, a humidity of 30–60% feels comfortable. Anything over this range is usually considered humid.

The higher the humidity, the more uncomfortable you’ll feel. Because humid air is so saturated with moisture, your sweat doesn’t evaporate efficiently to cool you off. That’s why you feel hotter and stickier on humid days.

Humid air is also harder to breathe, which can be a problem if you have asthma. In asthma, your airways become narrow. This narrowing makes it more difficult to pull enough air into your lungs. You may feel short of breath or cough and wheeze.

Breathing in humid air activates nerves in your lungs that narrow and tighten your airways.

Humidity also makes the air stagnant enough to trap pollutants and allergens like pollen, dust, mold, dust mites, and smoke. These can set off your asthma symptoms.

Dust mites live in furniture, carpets, and bedding. They thrive at humidity levels of 70–80%. Their dead bodies and waste can also set off asthma attacks.

Humidity over 60% also encourages the growth of mold. You’ll often find mold in damp places like bathroom ceilings and flooded basements. If you’re sensitive to mold, breathing it in can flare up your asthma.

The easiest way to tell if humidity triggers your asthma is to see if your symptoms flare up when the weather gets hot and sticky. Common asthma symptoms include:

  • trouble breathing or shortness of breath
  • coughing
  • tightness in your chest
  • wheezing

Though you can’t change the weather outside, you should keep the humidity in your home set to a comfortable 30–50%.

Here are a few other tips for controlling indoor humidity:

  • Turn on your air conditioner and close your windows. At night, when the temperature and humidity drop, you can open the windows to let in fresh air.
  • Install a dehumidifier. These devices pull excess moisture from the air.
  • Make sure your home has good insulation. Not only will it keep your home warm in the winter, but it’ll also keep it cool in the summer.
  • Turn on a fan in your bathroom, especially when you shower.

To prevent humid weather from triggering your asthma symptoms:

  • Avoid going outside on humid days, especially when the air quality is low.
  • If you do have to be outside, use your rescue inhaler before you go.
  • Don’t exercise outdoors during the hottest times of the day.
  • Drink lots of water and wear loose, light clothing when you’re outdoors.

Asthma treatment has three components:

  • avoiding triggers like humidity, mold, dust, and pollen
  • taking long-term asthma control medications
  • taking quick-relief (rescue) medications

Long-term asthma control medications taken every day help you avoid symptom flare-ups. These drugs include:

  • leukotriene modifiers such as montelukast (Singulair) and zileuton (Zyflo)
  • inhaled corticosteroids like budesonide (Pulmicort Flexhaler, Rhinocort) and fluticasone (Flonase, Flovent HFA)
  • long-acting beta2-agonists such as formoterol (Foradil, Performist) and salmeterol (Serevent)
  • combination inhalers such as budesonide-formoterol (Symbicort) and fluticasone-salmeterol (Advair Diskus)

Quick-relief (rescue) medications treat asthma attacks once they’ve started. These drugs include:

  • short-acting inhaled beta2-agonists like albuterol (ProAir HFA, Ventolin HFA) and levalbuterol (Xopenex)
  • ipratropium (Atrovent)
  • oral corticosteroids

While it’s hard to control the weather, you can reduce your exposure to humidity and avoid asthma symptoms in the process. Keep the humidity inside your home set between 30–50%. When it’s humid outside, stay indoors with your windows closed and your air conditioning turned on.

If you still have trouble controlling your asthma symptoms, even with medication, see your doctor. You probably need to review your asthma plan and make some modifications.