Though more commonly associated with short winter days, many people find they suffer from seasonal depression as the weather gets warmer. This mental health challenge is a clinical subset of seasonal affective disorder (SAD), and there’s strong evidence that poor air quality may be to blame.
What Is SAD
Seasonal affective disorder is straightforwardly defined by the Mayo Clinic as “a type of depression that's related to changes in seasons.” (Note that while SAD is still the popularly understood term, the American Psychiatric Association’s official designation is “Major Depressive Disorder with a Seasonal Pattern” or MDD-SP.)
SAD causes symptoms similar to classical depression, but the cold-weather and warm-weather varieties may be distinguished as indicated in the chart below:
| Fall & Winter SAD | Spring & Summer SAD |
|---|---|
| Oversleeping | Insomnia |
| Weight Gain/Increase in Appetite | Weight Loss/Decrease in Appetite |
| Low Energy/Fatigue | Agitation, Anxiety, & Irritability |
Source: Mayo Clinic
The cause of winter-onset SAD is no great mystery. Per the American Psychiatric Association, “SAD has been linked to a biochemical imbalance in the brain prompted by shorter daylight hours and less sunlight in winter.”
Summer-onset SAD is more difficult to untangle. One theory is that heat disrupts the body’s regulation of sleep cycles, resulting in depression. However, several studies point to another contributing factor—air quality.
Which Air Contaminants Peak During Spring and Summer?
Although air quality is usually worse during the winter, certain air quality problems accompany warm weather and thus may contribute to spring/summer SAD.
Wildfires: Per Consumer Reports: “On the West Coast of the U.S., [particle pollution] levels can spike over the summer because of wildfires[...]” According to a paper published in Nature, even short-term exposure to particle pollution “aggravates several psychiatric symptoms, including suicide attempts, increases emergency center visits, and hospitalization.”
Ozone: Ground-level ozone peaks during the summer months. This is because ground-level ozone is generated when sunlight hits other pollutants, especially vehicle exhaust. Since there is more sunlight in warmer months, there is more ozone. According to Environmental Health News, even low-level exposure to ozone has been linked with depression in adolescents. Also, “hospitals in cities with high levels of ozone pollution prescribe more antidepressants than other hospitals[...]”
Pollen: Allergy season is universally annoying, but for some, it might be more than that. Self-reported data suggests that those with pollen allergies are more susceptible to non-winter SAD.
Why Might Air Contamination Trigger Depression?
As we’ve seen, both pollen and air pollution may increase one’s risk of clinical depression, especially spring-onset seasonal depression. What causes this correlation?
One theory has to do with the body’s response to foreign contamination. Pollution and pollen trigger proinflammatory cytokines—proteins that are part of the body's immune response. However, studies indicate that these cytokines are also associated with depression. Individuals who are depressed have higher levels of proinflammatory cytokines in their bodies; furthermore, individuals whose proinflammatory cytokines increase due to other conditions sometimes acquire symptoms of depression. While more research is needed to determine if this link is causal or coincidence, it is suggestive.
Smaller particulate matter may trigger depression in another way too. PM2.5 is small enough to move through the bloodstream and penetrate the brain directly, creating what the aforementioned Nature article refers to as “structure changes.” This is particularly jarring in light of a recent study, which found that nearly every country in the world breathes unhealthy levels of PM2.5.
How Do I Reduce Air Contaminants?
While indoors, air purifiers can assist with particulate matter, pollen, and more. ActivePure pairs many of our devices with true HEPA filters (tested to capture at least 99.97% of all particle sizes). As a bonus, ActivePure Technology neutralizes many types of bacteria, mold, and viruses—both those captured by the filter and those out in the room.
