(CNN) -- You know spring has sprung when hundreds of people daily turn to Twitter to vent about their itchy eyes, dripping nose and uncontrollable sneezing and coughing. And if it's not obvious that allergies can ruin a person's day, watch how many tweets go by that use "allergies" and the f-word in the same sentence.
Seasonal allergies, which affect about 36 million Americans, aren't just an annoyance; many doctors agree there is a real connection between allergies and mood.
"'Cranky' is really the best word for it," says Katie Ingram, 30, of Alexandria, Virginia, a triathlete who suffers seasonal allergies. "I take a lot of medication for it and that makes me sleepy. And I can't do a lot of the things that I like to do outside, so that makes me cranky. ... The wheezing part of it makes me feel tired."
In some people, such annoyances are more serious. Research has shown there is about a doubling of risk for depression in a person suffering allergies and, if you've been seen by an allergist, that about triples the likelihood of having depression, said Dr. Paul Marshall, neuropsychologist at Hennepin County Medical Center in Minneapolis, Minnesota.
Those are correlations found in scientific studies, but they don't show that allergies cause clinical depression. In practice, allergy-connected mood changes usually boil down to mild depressive symptoms, like feeling sad, lethargic and fatigued, Marshall said. Some people say they're more likely to cry during the allergy season. Allergies could make symptoms even worse in a person with clinical depression, experts say.
"It's important for people to understand that experiencing allergies can affect their mood," Marshall said.
That's not to say that all people with allergies have depression or that all people with depression have allergies. But experiencing allergic reactions does seem to be a risk factor for developing depression -- not necessarily the emotional side of the condition, but more physiological symptoms such as low energy.
But is all of this in spite of the use of antihistamines or because of it? And is it the actual allergic reaction that causes these symptoms, or just the sleep disturbances and general discomfort?
The biological response
An allergic reaction is an immune response that releases cytokines, protein molecules used in communication between cells. When they signal the brain, they induce the feelings of sickness, or being "mentally drained," that often accompany the flu. This cytokine release isn't as powerful in allergies, but it's still present, Marshall said.
A 2002 study Marshall led, published in the journal Psychosomatic Medicine, found that allergic reactions to ragweed pollen cause "significant fatigue and mood changes" in at least some patients. Previous research Marshall collaborated on in 2000 found that such reactions could cause slowed speed of cognitive processing.
More recently, Dr. Teodor Postolache at the University of Maryland led a review published in 2008 of the association between suicidal indicators and allergies. Postolache's group noted a peak in suicide rates from April to June, and the dramatic environmental change of pollen that occurs during that time. The researchers found correlations between depression measurements and allergy symptoms in relation to the seasonal severity of tree pollen. In women the association is stronger between allergy, depression and suicide than in men, perhaps because allergy and depression are more common in women anyway.
Postolache's group has also explored cytokines that may be involved in triggering fatigue, hypothesizing that the allergic reaction is the direct biological cause of low mood.
This parallels what happens when stress gets you down, too, Marshall says.
A side effect?
Alternatively, low moods during allergy season could be situational -- the result of all the sneezing or side effects from medication.
Studies show that people don't perform as well at school because of allergic reactions, and adults' performance at work also suffers, says allergist Dr. Robert Overholt of Knoxville, Tennessee. These problems could exacerbate depressive symptoms, he said. That, combined with sleep disturbance, could make people feel unwell. Overholt doesn't believe the allergic response inherently triggers depression, but could circumstantially make existing depression worse.
"It would jump onto depression but wouldn't be the cause," he said.
Antihistamines themselves can also contribute to sleep disturbances and grogginess, he said.
Side effects of allergy medications can contribute to irregular sleeping patterns that increase irritability. The major antihistamines in pill form are now sold over the counter -- Allegra, Claritin and Zyrtec -- but they help only with sneezing, unless specified as the "decongestant" form. The added decongestant benefits come with a price, though. The same chemicals that ease your throat could also lead to insomnia, put more stress on the heart and lead to prostate problems in some men, Overholt said.
Erik Fisher, clinical psychologist in Atlanta, Georgia, sees more people fatigued this time of year, but isn't flooded with patients with allergy-fueled depression. He does see that allergies wear patients down, though.
"Once you realize what's causing your moods, it helps people feel less stressed out," Fisher said.
Children in particular are more susceptible to vast swings in moods and behaviors related to allergies because their bodies are more sensitive, Fisher said. In some kids, when allergies overwhelm the system, they have more temper tantrums and a harder time getting to sleep.
The bottom line, though, is that people shouldn't blame their allergies for deeper emotional issues, says Dr. Michael Silverman, assistant professor of psychiatry at Mount Sinai School of Medicine in New York. Even if some people have a direct mood response from allergies, that's not always the best explanation for feeling down.
"There's so much stigma associated with mood disturbance and anxiety that patients try to grab on to anything they can to explain what's going on," he said. "Allergies could be aggravating a problem in their lives they don't want to deal with."
What to do?
Intranasal steroids and topical antihistamines for the nose, which must be prescribed by a doctor, work pretty well, often in combination, and don't seem to cause drowsiness, Overholt said.
Others swear by the neti pot and other over-the-counter nasal rinses for sinus problems.
But the only way to get more complete, prolonged relief from allergies is to undergo desensitization, or what people commonly call "allergy shots," Overholt said. After an initial test to see what specific plants affect the patient, a doctor would administer small doses of the offending pollen or other substance to the patient under the skin over the course of three to five years.
At the end of that time, protection from allergies lasts another three to five years on average, with some people coming out allergy-free for life and others only getting relief for a year or two.
Allergy shots are the only longterm option for nixing the symptoms of allergies, and the fatigue and malaise that may accompany them, he said. Desensitization also prevents the formation of other allergies and reduces the risk of allergy-associated asthma.
Other forms of immunotherapy, such as oral (drops of allergens under the tongue) and intranasal (in the nose), have shown promise in trials, but are currently not available in the United States.
Ingram, whose allergies have been particularly bad in the last few years, is considering allergy shots. In the meantime, she vacuums every day, takes more showers, washes the sheets more and keeps the windows closed. Her husband, who doesn't have allergies, brushes the dogs more in the spring.
"My allergies are so bad right now, I would happily claw my eyeballs out with toothpicks to make that feeling go away," Ingram wrote on her blog.