Is the heating giving me a headache?

During the winter, it’s easy to get sick. Headaches, coughs and sniffles abound. Common colds, Covid and the flu are likely culprits. But sometimes these symptoms are exacerbated, or even caused, by the hot, dry indoor environments we inhabit during the colder months. Constant heating from boilers, heaters and furnaces can leave us feeling under the weather.

Dry air, decreased air circulation and increased exposure to indoor pollutants can make us feel drained and achy.

When it gets cold out, “people start coughing more when they’re indoors,” says Dr Imran Satia, a physician and assistant professor at McMaster University. Coughing, he explains, is a defensive mechanism. When Satia sees patients with a cough, the question is: what is the cough defending the lungs from?

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Of course, it’s possible that you’re sick. Studies such as one co-authored by Satia show you’re more likely to be infected with a respiratory virus during the winter. In this case, a cough is a spontaneous reflex that clears the lungs of germs and mucus.

But there are other reasons you might feel off once your indoor heating kicks in. Here’s what you need to know about how the heated indoor environments in our homes, offices and other spaces might be affecting you.

How does heated indoor air affect your health?

Overall, indoor air quality is not regulated and can vary depending on the type of building you live in, how old it is, how it’s heated and how much you can control the temperature.

In an effort to keep your home warm but your heating bill low, you might keep your windows and doors shut during the winter. However, this can cause indoor air quality to deteriorate, explains John Durant, a professor at Tufts University who studies indoor air quality. Pollutants like allergens, dust and mold may be released when heating systems turn on. These join other pollutants that end up indoors, like the chemicals in cleaning products, the byproducts of cooking and the compounds emitted by furniture. If your home isn’t well-ventilated and you keep the windows closed, these particles can cause irritation.

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When there’s not much air circulation and multiple people around, carbon dioxide can also build up, explains Dr Clayton Cowl, an occupational medicine specialist and pulmonologist with the Mayo Clinic. This can “cause headaches, fatigue and just not feeling right”, Cowl says.

Meanwhile, warm spaces can cause your heart rate to decrease and make you feel less energetic, Durant explains. Heated air is also dry, which can lead to dehydration.

“I think it’s fair to say that you’re kind of bombarding yourself with a mixture of environmental insults simultaneously when you heat your air, close your windows, dehydrate yourself and expose yourself to what’s present in your air ducts,” Durant says.

How does dry air affect us?

We’re already dealing with dryness in winter because cold air can’t hold as much moisture as warm air. When indoor air is heated, it becomes even drier. With these two effects combined, you can end up feeling like jerky.

“Cold, winter air holds less vapor than hot, summer air,” says Dr William Checkley, a physician and professor of medicine at Johns Hopkins University. “When your indoor heater is turned on, the air is heated, which in turn lowers relative humidity, making the air inside your home even drier.”

Dry air pulls moisture from your body and dries out your skin along with the mucus membranes inside your nose, throat and eyes, explains Checkley. These dry mucus membranes make us more susceptible to illness from airborne particles, including allergens, viruses and bacteria.

The drying out itself can also feel bad. When you breathe in dry air, the ensuing moisture loss can damage hair-like structures called cilia, which are on the cells that line your airway and propel mucus. This can make your throat scratchy. Dryness can also trigger the part of the vagus nerve that lines the throat, Satia says. All of this can lead to coughing.

Meanwhile, dehydration caused by dry indoor air can affect your blood circulation, causing fatigue. Scientists aren’t exactly sure why, but dehydration can also cause headaches. It’s possible that the “loss of body water may cause your brain to shrink, pulling it away from the skull and activating pain receptors”, explains Checkley.

How can you tell if warm indoor air is making you sick?

“The first thing I would say to anybody who’s coughing and feeling ill in the winter months is to make sure they haven’t got a virus,” says Satia. You can take an at-home Covid-19 test. If that’s negative and you still feel sick, in the US you can also ask your care provider for a multiplex PCR test, which can test for multiple viruses.

For people who can’t make it to a doctor’s office, Durant has a simple solution: go outside.

“If you feel like you’re sick because of indoor air, you can test that hypothesis really easily by going outdoors for a half-hour walk to see if you feel better,” he says. The walk won’t tell you what indoors makes you feel bad, but it’ll indicate that it’s something to do with your home rather than a virus.

What can you do to combat the effects of warm, dry air?

Drink more water – Checkley suggests about six to eight glasses a day. Your skin might also feel very dry; Checkley recommends moisturizing, which reduces water evaporation from the skin, and using a humidifier.

Related: Eight glasses of water a day excessive for most people, study suggests

You can reduce your chance of encountering allergens by regularly changing your bed sheets and being diligent about cleaning your floors, carpets and furniture. Technology like Hepa filters and air purifiers can improve indoor air quality. It’s also vital to regularly maintain the equipment that heats your home, Cowl says.

“People take that part of the house for granted,” he says. “They’ll remember to change the oil in their car, but they don’t have their furnace checked. And it’s potentially really important because you’re home a lot, especially if you work from home.”

Turning on a fan or opening some windows can also help – even if this seems counterintuitive in cold weather. “Anything you can do to increase or enhance the movement of air is bound to make you feel better,” says Durant.