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Our mood is influenced in many ways by our environment, and researchers have discovered a possible connection between the pollen in our air and a rise in suicide.

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In this episode we're going to be talking about suicide and suicidal ideation. If you need help, go to or call one of the hotlines in the description. 


We're all pretty much familiar with the winter blues, and many of us associate the coldest, darkest parts of the year with elevated rates of suicide. But what you might not know is that there are actually more suicides in spring and summer. And psychologists don't understand why yet.

They want to, in order to get help to the folks who need it, and they've identified one potential contributor to this phenomenon that you might not expect. Though of course every instance of suicide is its own unique situation and the result of many converging factors, there's evidence to suggest that in specific cases, allergies may contribute to this seasonal uptick. 

It's easy to understand why people might feel down in winter. The weather's cold, at higher latitudes the days are shorter, and the fun of summer vacation feels like it was decades ago. Things like Seasonal Affective Disorder, or SAD, can cause low mood around this time of year, too. For many people, spring and summer with longer days, warmer weather, and flowers coming into bloom are a cheerier time.

But unfortunately, it is not that way for everyone. Not everyone welcomes those blossoming spring flowers and their gift of pollen. In fact, research has consistently connected a larger number of suicides in spring and early summer to seasonal allergies. For example, in a 2005 study, researchers compared tree pollen data in the US and Canada from 1995 to 1998 with the national suicide data for the same years. They found that not only was the overall rate of suicide significantly higher when pollens were abundant, but the rate of suicide among women doubled in peak tree pollen season. In older women, the rate at this time of the year was four times higher.  

They also saw this effect in men, though not as strongly, and they note that the way we collect suicide data could be biasing the numbers. So it's not safe to assume that this only happens in women. 

Similar phenomena have been documented from Texas to Tokyo. Allergies are definitely capable of making people miserable, but that's not the same as experiencing suicidal thoughts or actions. Feeling sick alone isn't likely to be the cause of this fluctuation. And when researchers look more closely, they do in fact, find evidence that there's more going on.

The biological processes that take place in our body when we have an allergy may, in some people, be affecting their experience of suicidal thoughts or actions. One theory centers around inflammation, which is when your immune system tells your body to release a host of chemicals in order to protect your body from infections or injuries.

One group of these chemicals is known as cytokines. Cytokines are small proteins that carry messages between cells; they're involved in a number of biological processes such as reproduction, growth, and injury repair. But they're best known for their association with our immune systems, where the messages they carry can tell our brains that we are sick.  

Once your brain detects cytokines, it begins to react accordingly, inducing sickness behaviors. These range from fever to reduction of food intake. In some, it can trigger low mood and depression-like symptoms, making us withdraw from the world both physically and socially, maybe to try and help us recover from what's producing this cytokine response and making us ill.  

Since cytokines can literally change our behavior, that's led researchers to ask if there could be a link between the allergic response to airborne allergens, cytokines, and suicide. In a 2008 study, when researchers sensitized and exposed rats to allergens in the air, their behavior became observably more anxious and aggressive in response to stress, compared to controls. 

Another 2008 study looked directly at dissected rat brains to see if there were any clues as to what might be sparking that kind of behavior at a molecular level. And they found that inducing an immune reaction upped the amount of cytokines in certain areas. In particular there was increased expression of specific cytokines in the brain stem and hippocampus of female rats.

In another study published around the same time, the same research group examined the brains of suicide victims and found those same cytokines were elevated in their prefrontal cortexes, though statistically the numbers were underwhelming. In particular, the orbitofrontal cortex had high levels of cytokines. This is an area already known to be involved in regulating our behavior, from impulsivity to suicidal actions. It's also been implicated in feeling hopeless.  

It seems that cytokines interfering with activity in this area of the brain, at least in folks who are already predisposed, may play a part in these spring and summer suicides. This isn't to say that you should be afraid of pollen season. Suicide is typically the result of multiple contributing factors. It's just that for some people, pollen-based cytokine activity may cause increases in suicidal thought. Mitigating the risk allergies pose likely isn't just a case of prescribing anti-allergy pills, though researchers are investigating their application. Unfortunately, some of those medications may also induce suicidal feelings as a side effect.

Allergen and cytokine activity isn't the only theory as to why there's an increase in suicides at this time of the year though. Suicide is a really complex phenomenon, and it wouldn't be accurate to say allergies are the only cause of the spring and summer seasonal uptick. Like, we don't know the link with allergies is causal, even though the cytokine mechanism makes sense. There could be other factors present in spring and summer that contribute.

Our moods are influenced in powerful ways by things like environmental, psychological and social factors. And psychologists will continue to do research in all of these areas to find any risks that can be mitigated to prevent suicides from happening. Without research, the role of allergies might have flown under the radar, but thanks to continued curiosity and study, we're on the path to, hopefully, saving more lives.

Thanks for watching this episode of SciShow Psych. Please remember that if you need to talk to someone, whether about suicidal thoughts or other mental health conditions, there are people that are here to listen and help you through. We've included some contact numbers and resources in the description below, so please make sure to use them if you need to.

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