Is It Safe To Keep Hiking in Wildfire Smoke?

POV: You spent years planning your thru-hike of the Pacific Crest Trail, only to have your dreams of a continuous footpath squashed by the wildfires that have closed large swaths of the trail.

Sadly, this is not a hypothetical scenario: it’s the reality of life for the PCT’s Class of 2024. Some 300 miles of the PCT have been closed due to encroaching blazes this summer, and fire season is far from over.

“The sky was a violent shade of orange. I couldn’t see more than twenty feet ahead of me,” writes PCT hiker and Trek blogger Abby Evans of the nightmarish conditions they encountered near Chester, California this summer.

Evans was ultimately forced to skip 160 miles of the PCT to avoid a fire closure. Jumping north wasn’t an easy decision, but their hands were tied: a closure is a closure.

Elsewhere on the trail, hikers are weighing a different sort of decision. What should one do when the trail is smoky but technically still open? Is it safe to keep hiking amid diminishing air quality?

Health Impacts of Wildfire Smoke Exposure

Photo: Abby Evans

As the Pacific Crest Trail Association (PCTA) points out in a blog post, “Smoke is unhealthy even when it’s not an immediate threat to life.” The haze can contain pollutants like carbon monoxide, formaldehyde, benzene, and particulate matter that objectively aren’t great to inhale.

Exposure to wildfire smoke has been shown to exacerbate respiratory conditions (asthma, COPD, etc.), increase rates of respiratory and cardiovascular diseases, and — according to a growing body of evidence — increase mortality from all causes. Smoke exposure may also affect birth outcomes in pregnant people.

And because smoke plumes can travel hundreds of miles, these effects can be felt even if the fire itself is far away. “Wildfire pollution can affect people over an area 10 to 15 times larger than the actual fire,” explains Dr. May-Lin Wilgus, a pulmonologist at UCLA Health and an associate clinical professor at the David Geffen School of Medicine at UCLA.

We can all agree that breathing smoke is probably not great for our health.  Indeed, the prevailing health advice is to stay inside on smoky days and avoid vigorous activity to protect your lungs. According to AirNow.gov, “Everyone in a smoky area should avoid strenuous work or outdoor exercise to the greatest extent possible.”

Cool story, bro.

A 2023 thru-hiker celebrates reaching the PCT’s northern terminus on a smoky day. Photo: Scorpion Queen

Yet that is precisely what people tend not to do. Several recent studies found that smoky air had little impact on peoples’ outdoor recreation plans. Interestingly, visitation rates at campgrounds and national parks remained high even during smoky periods.

The findings of one study suggest that “most of the total welfare losses accruing to campers due to smoke occur via health impacts from trips taken in spite of smoky conditions, rather than due to canceled trips.”

In other words, most people seemingly would rather suffer hazy orange skies and scratchy throats than cancel their expensive and long-anticipated national parks vacation.

 It makes sense that long-distance hikers would feel much the same way. When you’ve poured your heart and soul into the dream of thru-hiking, when you’ve likely already got hundreds of miles under your belt and have grown accustomed to hiking through rain and snow and blistering sun, are you really going to let a little bad air deter you?

Look, we’re human beings. We’re not great at weighing long-term health outcomes that may or may not even happen to us against immediate wants and needs.

It’s like this. Yes, hiking in smoke might make my asthma worse. Yes, it might put me at increased risk of developing cardiovascular disease. But those things also might not happen. Whereas if I get off the trail because of the air quality, the smoke definitely will derail my thru-hike and force me to change all my plans, goals, dreams, aspirations, etc. Is the math mathing yet?

Understanding Exposure Levels

Smoke along the Washington section of the PCTA in 2017. Photo: Alex Shapiro

Many of us live in semi-polluted environments, but smoke pollution is different. “A big part of the danger of wildfire pollution is the intensity of the exposure,” says Wilgus, the UCLA pulmonologist. “The amount of pollution released can be many-fold higher than the routine air pollution we’re exposed to from other sources.”

What’s the difference between a day hiker breathing smoky air for a single afternoon, a tourist camping amid poor air quality in Yellowstone for four nights, and a thru-hiker inhaling smoke 24/7, potentially for weeks on end?

The truth is we don’t know. No one is studying health outcomes in long-distance hikers breathing smoky air. There just aren’t enough of us for large-scale studies to make sense. In short: who cares? (Other than ourselves and our moms, I mean.)

A friend of mine drew a comparison between wildland firefighters (her occupation) and thru-hikers. By no means is this a perfect analogy. But like firefighters, hikers exert themselves all day and then sleep outside all night.

AirNow.gov says outdoor workers are at elevated risk of negative health outcomes due to smoke, because they may spend extended periods exposed to high concentrations of wildfire smoke.

The Occupational Safety Hazard Administration (OSHA) has standards in place to protect firefighters and other outdoor workers in smoky conditions (even those standards could arguably be stricter, but that’s another conversation). In contrast, thru-hikers voluntarily assume the health risks associated with smoke, often without data to inform that choice.

What the PCTA Says

Smoke viewed from the northern California section of the Pacific Crest Trail in July 2024. Photo: Abby Evans

Jack Haskell, Trail Information Manager for the Pacific Crest Trail Association (PCTA), encourages hikers to review his organization’s guidance for its own staff and volunteers working in smoky conditions.

This document advises trail crews to base work decisions on the US Air Quality Index (AQI)*. “Any amount of time in unhealthy categories … constitutes evacuation criteria. If the AQI is above 150, leave the field as soon as possible.”

Trail crew members may increase their air intake to 10 to 20 times above normal, increasing their exposure to pollutants. It’s safe to assume that the same would be broadly true for hikers.

This is not an official recommendation from the organization, but if we were to apply the PCTA’s trail crew guidance to hikers, it would look something like this:

• AQI 51-150: Maybe don’t hike today
• AQI above 150: Definitely don’t hike today
• Are you under 18, over 65, a smoker, or someone with a chronic lung disease like asthma or COPD? You’re at higher risk and should err more on the side of caution when deciding whether to hike
• NIOSH N95 and P100 masks: They can help reduce smoke inhalation when worn correctly, but “this is only a single mitigation measure and should not be thought to render dangerous conditions safe,” according to the document
• Learn to recognize symptoms of smoke exposure, including coughing, trouble breathing, stinging eyes, scratchy throat, fast heartbeat, and lingering fatigue

*The US Fire and Smoke Map is the best resource for anyone wanting to monitor air quality throughout the country.

“Flexibility is key.”

Smoke from wildfires in Nova Scotia traveled far enough to obscure views from the AT in Pennsylvania in 2023. Photo: Peg Leg

 No one wants to hear this, but hiking through smoky conditions isn’t the best idea. Smoke inhalation can have serious consequences beyond just eye and throat irritation.

“Every year, I see an influx of patients with asthma and COPD whose symptoms are exacerbated by wildfires,” says Wilgus. “I see the devastating toll wildfire pollution takes on my patients, many of whom describe lingering symptoms for months.”

If you can afford some time off to see if the smoky conditions will pass, do that. Or jump to a section with better air quality. Many of us hit the trail to have fun, enjoy nature, and look after our physical and mental health. Is hiking in a dystopian smokescape really ticking any of those boxes?

“Err on the side of caution for your physical health,” Haskell tells The Trek via email. “The trail will still be here next year and the years after; come back when wildfire and smoke aren’t ruining your experience and threatening your wellbeing.”

Evans, the PCT Trek blogger, echoes this sentiment in their blog. “If I learned anything from this experience, it’s that when life sets your future plans on fire, it’s time to get moving … The PCT is teaching me to figure out what I truly want — quickly.

“Flexibility is key to having an enjoyable and fulfilling thru-hike. No summer is wasted spending time outside. Just because you can’t hike a continuous footpath does not mean you can’t have a fulfilling and fun time. It’s not a bad thing; it’s just different.”

Featured image: Smoke seen from the PCT in northern California in July 2024. Photo: Abby Evans