As a series of massive fires continues to blaze through the Los Angeles area, blanketing neighborhoods with smoke and forcing thousands of people to evacuate their homes, air quality remains unhealthy throughout many parts of the county.

Wildfire smoke is a mixture of water vapor, gases, and microscopic particles known as particulate matter. The smallest of these particles, known as PM2.5 because they have a diameter of less than 2.5 micrometers, pose the most danger to human health. They can lodge deep in the lungs and sometimes enter the bloodstream. Earlier this week, PM2.5 around Los Angeles rose to “hazardous” levels, the highest warning on the US Air Quality Index.

“Wildfire smoke is risky for everybody, especially when the particulate matter that is being released is in large quantities for long periods, like what is happening in California right now,” says Zachary Rubin, a Chicago-area pediatrician and spokesperson for the American College of Allergy, Asthma, and Immunology.

When fine particulate matter is inhaled, it can trigger inflammation in the body. Symptoms can range from the mild, such as burning or itchy eyes, runny nose, scratchy throat, and headache, to severe respiratory issues, including difficulty breathing, wheezing, coughing, fatigue, and chest pain. It can take anywhere from a few hours to days after exposure for symptoms to appear. In the most serious of cases, it increases the risk of premature death.

Children, older adults, pregnant individuals, and those with heart or lung conditions or weakened immune systems are at higher risk of developing severe side effects. But Rubin says it’s possible for anyone, regardless of their health status, to have respiratory effects from exposure to wildfire smoke.

“Any level of air pollution, including from wildfires, can be dangerous for your health,” says Laura Corlin, an environmental epidemiologist at Tufts University School of Medicine. Just how dangerous depends on many factors, including your existing health status, your proximity to the fire, and the duration of exposure. “A good rule of thumb is that more exposure is worse,...