The amount of moisture in the air changes with the temperature. This is known as relative humidity. Your home’s relative humidity should normally hover around 40%. However, a home’s HVAC system as well as the weather affect the overall relative humidity.

During the hottest and coldest times of year, moisture levels in outdoor air decreases, causing health issues for sensitive people. Dry air can also affect your Indoor Air Quality (IAQ) and make you sick or miserable. You might quickly notice when indoor air gets too dry. You feel thirsty, your nose is clogged and your skin is parched.

What makes indoor air become too dry?

When temperatures fall outside and cold, dry air blows in through open windows or doors, relative humidity drops drastically. The colder air is, the more it contracts and the fewer particles of moisture it can hold. 


Extreme heat can also reduce the moisture in the air. Heat makes air expand and normally allows it to hold more moisture. But in a hot climate with little rain, like a desert, moisture in the air quickly evaporates.

Your indoor habits can cause even more dry air problems inside. Turning on a central heating or air conditioner system forces dry air into your home. This makes the air in your home even drier.

The health effects of dry air

Dry air can make it easier for bacteria, viruses and allergens to spread and get into your body. Many of us spend 80% of our time indoors every day, so it’s important to know when the air around you is too dry.

Your respiratory system, which includes your nasal passages, throat and lungs, is coated with fluid that protects you from airborne irritants. Breathing dry air can thin out this fluid. This makes it easier for your airways to become swollen, irritated or infected.

Cold air also triggers your body to produce histamine. The combination of cold temperatures and dry indoor air can then have effects on your health, including:

• Coughing, wheezing and runny nose
• Dry or sore throat, nosebleeds and dry, flaky skin
• Feeling congested, thirsty or tired
• Increased asthma symptoms, as cold air is an asthma trigger


These problems are also common with allergies, colds and the flu, so dry air may not always be the cause. But if you start noticing them when the weather cools down or only when you’re inside, dry indoor air may be the reason. Dry air can make it easier for the flu and other viruses to spread.

How can I prevent dry air problems?

Actions you can take to protect yourself from dry air problems include:

1. Monitor your relative humidity (RH)so that you know exactly when indoor air gets too dry or too humid.
2. Use your HVAC system and a humidifier to keep humidity levels in your home around 40%.
3. Turn fans low or completely off, especially at night.


Indoor dry air can be caused by problems both inside and outside your home. But there’s plenty you can do to minimize indoor dry air problems that affect your health.