The other day, I was working at a store in my neighborhood and had a really beautiful but heavy conversation with a customer. Her adult son, married with a baby, died by suicide a month prior. For her privacy, I won’t reveal any other details, but we had a meaningful conversation about the things we can do to prevent suicide. In line with her experience, she reminded me that suicide rates peak in the spring and summer, prompting me to do some research.

According to a study of almost 6,000 English-speaking adults living in the US between 2001 and 2004, a history of seasonal allergies was correlated to suicidality (Messias et al, 2010). Another study out of Germany reported that individuals with seasonal allergic rhinitis (SAR) showed a “season-dependent increase in depressive symptom[s]” (Trikojat et al, 2017).

There was a lot of clinical information about the process, but my (non-professional) interpretation is as follows. An immune protein score was measured in these individuals and “correlated with a higher severity of other inflammat[ion].” The influence of these proteins on emotion and depression might be because they’re able to cross the blood-brain barrier by traveling through the nasal cavity to the central nervous system. Meta-analyses demonstrated that levels of this protein, IL-6, are consistently higher in patients with major depression and in otherwise healthy participants who received the protein via vaccination or bacteria. The association between inflammation and depressive symptoms could be because these proteins inhibit the biosynthesis of serotonin, leading to a reduced availability of serotonin which is considered to be a key factor in the pathophysiology of depression. Previous research supports this by showing that reduced levels of serotonin occur during phases of acute allergic inflammation. Also, allergies and SAR can cause disruptions in sleep, further impacting depressive symptoms.

A few more studies I reviewed (Coimbra et al., 2016) (Postolache et al., 2010) (Christodoulou et al., 2012) confirmed that suicide rates peak in the springtime. Another reason for this, besides inflammation that inhibits serotonin synthesis, could be other brain-chemical reactions to light and increased exposure.

The biological processes probably aren’t the takeaway here. Whatever the reason, people are experiencing significant depression in the spring, despite the societal optimism that we think spring ushers in. Keep that in mind, and tell your friends and family that depression and suicidality can increase in the springtime. Check in on them and yourself.

It was important to me to do this research personally, too. It was a rough few weeks; I experienced a serious bout of depression that seemingly came out of nowhere… until this topic came up. I realized my decreased mood coincided pretty darn closely with an uptick of allergies concluding in a nasty sinus infection. The evidence is sparse still… though I can’t help but associate the two. Makes me feel a little less crazy.