Millions of Americans suffer from seasonal allergies, and a growing body of research suggests there may be a link between those allergies and mood disorders like anxiety and depression, Christina Caron reports for the New York Times' "Well."

How allergies can affect your mental health

Allergies can affect a person's sleep, energy levels, sense of smell, mental sharpness, and their productivity — which can ultimately impact their mental health, according to David Gudis, chief of the division of rhinology and anterior skull base surgery at  New York-Presbyterian/Columbia University Irving Medical Center.

"Anytime you don't feel well, that's a psychological stressor," he said.

Experts believe that, since allergic rhinitis — also known as hay fever — is an inflammatory disease, inflammation could impact the brain.

For example, when someone is allergic to tree pollen, the pollen reaches membranes lining the nose, which prompts an immune system response of a variety of substances that can create inflammation in the body's airways and brain, Caron reports.

"Among these substances are proteins called cytokines, which the body produces to fight certain infections," said Todd Gould, a professor of psychiatry at the University of Maryland School of Medicine. "These cytokines activate areas of the brain that regulate depression and anxiety."

In a study of mice and rats, Gould and colleagues exposed the rodents' noses to allergens repeatedly, and later dissected their brains. They found the rodents showed signs of anxiety and saw an increase in cytokine production within their brains, as well as higher levels of a stress hormone.

Other studies have found similar links between allergies and mood disorders. One study found that people with allergies are about one and a half times as likely to have major depression, while another study  found a similar link that was especially pronounced in women.

Other observational  studies  have found allergies to be associated with a high risk of anxiety, and researchers in Taiwan  found  that allergies were associated with a higher risk of psychiatric disorders in adults.

Meanwhile, a handful of studies have suggested there could be a link between high pollen counts and suicide risks; however, Caron reports the potential association between the two is not yet well understood.

"We should keep in mind that suicide risk involves many different risk factors," said Christopher Lowry, an associate professor of integrative physiology at the  University of Colorado, Boulder. Future research should look at the specific role allergens may play in influencing a person's behavior, he added.

When you should see a doctor

When you're suffering from allergies, it can be difficult to determine whether you're suffering from depression or if you're feeling "so tired because my body is sick," said Philip Muskin, a professor of psychiatry at  Columbia University Irving Medical Center.

According to Muskin, if you aren't feeling yourself, you should speak with your allergist or your primary care provider and be as specific as you can about your symptoms and how long they've been going on.

You should also talk to your doctor about any allergy medications you're taking, as some can affect your mood, Gudis said.

Antihistamines used in NyQuil or Benadryl can be sedative and make people feel "out of it," Muskin said. In addition, oral corticosteroids like prednisone, often used to treat severe allergies, can cause irritability or increase a person's risk of developing symptoms of anxiety or depression. Similarly, nasal decongestants like the ones found in Sudafed or Sudafed PE can cause anxiety, nervousness, and insomnia. (Caron, "Well," New York Times, 5/8)