Smoke is a common sight in the northeastern United States, whether you live there or just use social media. The smoke is settling in cities like New York, Philadelphia and Baltimore, which are sepia-toned from the wildfires raging across Canada. For residents, the affected air quality (which as of Wednesday was measured at 14.5 times the World Health Organization’s air-quality-guideline value) is leading to symptoms induced by both the actual conditions and the stress of the situation–including some severe headaches.

Doug Laher, Chief Executive Officer of the American Association for Respiratory Care, says that increased blood pressure and elevated heart rate can cause headaches. Michael Rubino, an expert in indoor air quality, says that the current concentration of smoke as well as the unprecedented amount airborne particles can make even the healthiest person feel unwell. Poor air quality can lead to sinus inflammation and oxidative stresses, which both cause headaches.

The presence of PM (particulate matter) is a major factor in determining the air quality level. These are tiny particles that can be inhaled and bypass our bodies’ self-defense mechanisms, making their way to our bloodstream. According to the EPA these particles are classified into PM10, which are particles with a diameter less than 10 micrometers, and PM2.5, which are fine particles with a smaller diameter, less than 2.5 micrometers. Add to this the chemicals found in wildfire smoke, such as aldehydes and acid gases (such as sulfur dioxide, nitrogen oxides and carbon monoxide), and symptoms such a coughing, scratchy throats, shortness and headaches are a natural reaction.

So how do we deal? Rubino says that staying inside is the best option to protect your system from smoke contamination caused by wildfires or when the AQI reaches 150. Wear an N95 mask when going outside, regardless of the reason. This will help reduce your exposure to particulate matter.