As the embers of the Los Angeles wildfires finally begin to cool and some residents cautiously return to their homes, a new threat emerges—one that is invisible to the naked eye but no less dangerous. The air inside these seemingly untouched structures may be harboring a toxic cocktail of smoke, ash, and chemicals that can pose significant risks to health. Experts warn that even homes spared from physical damage are not immune to the insidious effects of poor air quality.

Katherine Pruitt, the national senior director for policy at the American Lung Association, emphasizes the gravity of the situation. "There’s a lot that has potentially happened to affect poor air quality in your home, even if you haven’t suffered any physical damage to the home itself," she says. "The fumes and the ash, the particles that are going to be in your indoor environment, are not safe to breathe. You especially don’t want to come into contact with the ash in your lungs, eyes, or skin."

The Los Angeles Public Health has declared a local health emergency for the entire county due to the fires, implementing measures such as prohibiting the use of air blowers, including leaf blowers, to reduce health risks associated with ash and particulate matter from smoke. Wildfires, in their destructive path, burn more than just trees and grass; they release a myriad of toxic chemicals from burned cars and structures. Even after the fires subside and the smoke clears, these chemicals can linger, absorbed by walls, floors, furniture, and other indoor surfaces, off-gassing for weeks or even months.

The American Lung Association’s State of the Air report for 2024 has listed the Los Angeles area as one of the top 10 cities polluted by year-round particle pollution, a ranking that has been consistent for decades. With the wildfires exacerbating the situation, the air quality index has been at "unhealthy" levels for many parts of Southern California for several days. Toxicological and epidemiological studies suggest that particle pollution from wildfires is more harmful to the respiratory system than equal doses from other sources. Exposure to such pollution can cause eyes to burn, noses to run, and can embed deep in the lungs, leading to breathing problems such as bronchitis. Moreover, these minuscule particles can enter the bloodstream, causing inflammation and aggravating conditions like diabetes and chronic heart disease.

A 2024 study of the Marshall Fire in the Boulder, Colorado, area revealed a startling reality. Even after the smoke had cleared, researchers found elevated levels of metals and polycyclic aromatic hydrocarbons (PAHs) in ash, in addition to volatile organic compounds (VOCs) in air samples inside homes. VOCs can be toxic to humans, with at least one VOC, benzene, known to cause cancer. Exposure to PAHs is also associated with an increased incidence of cancer, according to the World Health Organization. Residents surveyed in the Boulder study reported symptoms related to smoke and ash, including headaches, coughing, sneezing, sore throat, and watery eyes, even six months after the 2021 fire. Those living closer to burned-out buildings experienced more severe symptoms. While the number of people reporting symptoms declined a year after the fire, about a third of those surveyed still reported at least one smoke- and ash-related symptom two years later.

In the face of such risks, there are steps that residents can take to mitigate exposure to these harmful substances. The US Environmental Protection Agency recommends checking HVAC filters every few days and changing them if they appear dirty. A clean filter is significantly more effective at protecting indoor air quality. For those with HVAC systems equipped with a high-efficiency filter (MERV-13 or higher), running the system’s fan as often as possible by setting it to "On" rather than "Auto" can help. Portable air cleaners, particularly those with HEPA and charcoal filters, can also be beneficial. The EPA suggests placing air cleaners in rooms where people spend the most time and running them on the highest fan speed until any lingering smells dissipate.

To further protect indoor air quality, it is advisable to limit activities that can generate additional fine particle pollution, such as frying or broiling food. Avoid vacuuming unless the vacuum is equipped with a HEPA filter, and refrain from smoking or vaping indoors. While the temptation to use candles or incense to mask the lingering smell of smoke may be strong, these should be avoided as they only contribute to more particle pollution. When cleaning, opt for soap and water over aerosols or chemical cleaners that may react with the chemicals in ash. Traditional vacuums or brooms should be avoided as they can stir up tiny particles into the air. If using a vacuum with a HEPA filter, mist surfaces with water first to prevent ash from becoming airborne.

During cleanup, it is crucial to take protective measures. Wear gloves, goggles, long sleeves, long pants, and socks to shield the skin, and use a N95 or P100 respirator mask to prevent inhalation of ash. "Not a surgical mask. Not a cloth mask. Those aren’t good enough to keep out those very fine particles and some of the gases that you might need to worry about," Pruitt advises. Ash should be washed off the skin promptly, and clothes should be changed before leaving a cleanup site to prevent tracking ash into cars or other locations.

Certain populations are particularly vulnerable to the effects of particle pollution and should avoid ash cleanup work altogether. This includes individuals with heart or lung diseases like asthma or COPD, the elderly, children, and pregnant people. Their bodies have a harder time expelling pollution from their lungs. Pets should also be kept away from ash, as they are more susceptible to illness. If pets do come into contact with ash, their paws should be washed immediately.

In conclusion, the aftermath of wildfires presents a complex and ongoing challenge to public health. The invisible threat of poor indoor air quality requires vigilance and proactive measures to protect the health of residents and their communities. As the cleanup efforts continue, it is essential to remain informed and take necessary precautions to mitigate the risks associated with smoke, ash, and toxic chemicals. By doing so, we can begin the process of healing and rebuilding, not just our homes, but our health as well.