May 25, 2010 (New Orleans) -- If you suffer from a mood disorder and hay fever, don't be surprised if your mood worsens when pollen season rolls around.

Preliminary research shows that people with depression or bipolar disorder who are allergic to tree or ragweed pollen experience worse depression when exposed to that allergen.

"The worse the allergy symptoms, the worse their depression scores [on a standardized test used to assess depression and mania]," says researcher Partam Manalai, MD, of the department of psychiatry at the University of Maryland School of Medicine in Baltimore.

The findings were presented at a news conference here at the annual meeting of the American Psychiatric Association (APA).

Studies show that as many as one in 10 Americans suffers from depression. As many as one in five may have seasonal allergies, or hay fever, Manalai tells WebMD.

Some studies suggest that people with hay fever are prone to mood disorders, he says.

Interestingly, there is a springpeak in pollen count due to tree pollen -- and a somewhat smaller fallpeak due to ragweed -- that parallels a spring peak and a somewhat smaller fallpeak in suicide rates across the world, Manalai says.

To further explore the relationship between hay fever and allergies, the researchers recruited 100 individuals who had been diagnosed with depression or bipolar disorder. Of the total, 53% tested positive for allergies to ragweed or tree pollen.

In people with allergies, scores worsened substantially from low pollen season to high pollen season. The worse their allergy symptoms, the greater the change.