It’s best to stay out of the smoke!

Wildfires and urban fires have at least one thing in common: smoke.  Although the smoke from each is different, scientists agree that it can harm your body in a number of ways apart from the immediate respiratory effects, which are becoming more apparent with each new study.  According to an early 2025 Stanford review, Wildfire smoke is about 10 times as toxic as the regular air pollution from the burning of fossil fuels, and there's no safe level of exposure, Stanford experts say: the more we breathe, the worse a range of health outcomes. (What we know about the health effects of wildfire)  We wanted to take the time to highlight the latest research about smoke’s effects on the different parts of the body.

• Smoke affects your immune cells: In a 2025 study of 31 smoke-exposed adults (firefighters and civilians) and 29 non-smoke exposed adults, blood samples showed that the smoke-exposed individuals had cellular-level changes.  These included elevated levels of 2 types of immune cells, changes in 133 genes related to allergies and asthma, and more immune cells bound with toxic metals like mercury and cadmium.  This meant that “the immune system is extremely sensitive to environmental exposures like fire smoke, even in healthy individuals."

• Smoke affects your mental health: As studied during July and December 2020 in California, exposure to wildfire smoke substantially increased mental health Emergency Department visits.  A 10 microgram/m3 increase in wildfire-specific PM2.5 was linked to a higher number of visits, including for depression, anxiety, and other mood-affective disorders, for up to seven days post-exposure.

• Smoke may cause and/or exacerbate Alzheimer’s Disease (AD): Alzheimer’s disease is a progressive neurodegenerative disorder with largely unknown origins and no known cure. There is a growing body of literature which relates woodsmoke-generated and ambient air pollution particulate matter exposure to Alzheimer’s disease (AD) onset or exacerbation. (Influence of Woodsmoke Exposure on Molecular Mechanisms Underlying Alzheimer’s Disease: Existing Literature and Gaps in Our Understanding)

• Smoke affects men’s fertility:  In a 2021 study, researchers showed that exposure to smoke from Douglas fir needles induces sperm DNA methylation changes in adult mice.  DNA methylation is a biological mechanism that can regulate how a gene is expressed, kind of like a dimmer switch on a light bulb. Environmental factors can influence DNA methylation, and this can be harmful if it occurs at the wrong time of life or at the wrong gene. (Breathing wildfire smoke can affect the brain and sperm, as well as the lungs)  It is indicative of overall male reproductive health as it has been associated with abnormal sperm counts and motility, and may also act as a biomarker of multigenerational disease risk. 

• Smoke affects your pregnancy: During pregnancy, respiratory rate increases 40%, meaning that more smoke gets inhaled.  According to a study assessing prenatal exposure to wildland fire smoke for live single births in California conceived from 2007 to 2018, a total of more than 5 million babies, people living somewhere that had a wildfire smoke PM2.5 concentration of 10 micrograms per cubic meter higher than what other people experienced at that stage of pregnancy had approximately a 3.4% higher risk of preterm birth. (Exposure to wildfire smoke during pregnancy increases risk of preterm birth)

• A 2024 study identified a significant association between exposure to open fire (including wildfires, mountain fires, coal mining fires, and slash-and-burn agriculture) and increased risk of pregnancy loss in India, Pakistan, and Bangladesh.  Additionally, occupational exposure to fire was associated with increased risk of miscarriage and preterm birth. (Maternal and Child Health Among Female Firefighters in the U.S.)

• Smoke affects your baby: Scientists studied breeding monkeys that were in direct exposure to smoke from the the California Campfire wildfire that razed the town of Paradise in November of 2018, during the peak of their 2 week breeding season.  They concluded that toxins in wildfire smoke may cause birth defects by acting through the placental–adrenal–brain axis  in higher primate species, including humans.  Some of the Campfire smoke-exposed baby monkeys exhibited statistically significant deficits in both adrenal development/function and alteration in neonatal temperament.  (Early exposure to wildfire smoke can lead to birth defects)  In addition, a 2021 study showed that the offspring of maie rats exposed to biomass (plant/wood) smoke exposure demonstrated decreased exploratory behavior, locomotor activity, and spatial navigation, as well as increased anxiety levels.

• Pregnancy during the 2003 Southern California wildfires was associated with slightly reduced average birth weight among infants exposed in utero. These weight differences were 7.0 g lower when the wildfire occurred during the third trimester, 9.7 g lower when it occurred during the second trimester, and 3.3 g lower when it occurred during the first trimester. (Birth Weight following Pregnancy during the 2003 Southern California Wildfires)

Fire is such an unpredictable thing…sometimes.  Sure, you never know when a local building will catch fire due to accident or arson, but there are climates that are prone to drought, and as droughts wear on, fire risk increases as plants and vegetation dry out and lightning strikes may increase.  If you have any indication that wildfire smoke will be a problem in your area, make sure to get extra MERV 13 filters for your central AC (let us know your air handler model number, and sizes (in inches) of your return filter(s) so we can make sure your system can handle MERV 13 filtration), and/or purchase at least 1 stand-alone HEPA filter for each occupied bedroom at night.   We like the Medify brand of purifiers for their value and effectiveness, but there are many other brands available.  Alternatively, you can gather the supplies to make your own purifier(s).  This video from Dean Corsi uses (4) 2" 20x20 Merv 13 filters, a box fan, and some tape. Here are some 1" filters, here are some 2" filters, and you can also use our Activated Carbon Media on any fans or in addition to filters, to remove smoke odors and VOCs.   Alternatively here are some 4" filters ( for a slim design, just tape it on the back of the fan instead of making a box, this is actually the most economical for filters).

Photo by Nick Nice on Unsplash