Kids who have allergies at an early age are more likely than others to also have problems with anxiety and depression, according to a new study.

As the number of allergies increase, so do internalizing behavior scores, the researchers found.

Internalizing behaviors include disorders, like anxiety or depression, that develop when people keep their problems to themselves, or "internalize" them.

"I think the surprising finding for us was that allergic rhinitis has the strongest association with abnormal anxiety/depression/internalizing scores compared to other allergic diseases," said lead author Dr. Maya K. Nanda of the division of Asthma, Allergy, and Immunology, at Children's Mercy Hospital in Kansas City, Missouri.

Rhinitis includes the "hay fever" symptoms of runny nose, sneezing and itchy, watery eyes.

The researchers studied 546 children who had skin tests and exams at age one, two, three, four and seven and whose parents completed behavioral assessments at age seven. They looked for signs of sneezing and itchy eyes, wheezing or skin inflammation related to allergies.

Parents answered 160 questions about their child's behaviors and emotions, including how often they seemed worried, nervous, fearful, or sad.

Kids who had allergic sneezing and itchy or watery eyes or persistent wheezing at age four tended to have higher depressive or anxiety scores than others at age seven, the researchers reported in Pediatrics.

Anxiety and depression scores increased as the number of allergies increased.

"This study can't prove causation. It only describes a significant association between these disorders, however we have hypotheses on why these diseases are associated," Nanda told Reuters Health by email.

Children with allergic diseases may be at increased risk for abnormal internalizing scores due to an underlying biological mechanism, or because they modify their behavior in response to the allergies, she said.

Like other chronic diseases, allergic diseases may trigger maladaptive behaviors or emotions, she said, but some prior studies support a biologic mechanism that involves allergy antibodies triggering production of other substances that affect parts of the brain that control emotions.

Earlier studies have found links between allergies and anxiety disorders such as panic attacks or generalized anxiety disorders, Nanda said.

The new study took race, gender and other factors into account, "so the strong association between allergic disease and internalizing disorder we found is definitely present," she said.

The severity of mental health symptoms varied in this study. Some children had anxiety and depression that needs treatment, while others were at risk and required monitoring, she said.

"We think this study calls for better screening by pediatricians, allergists, and parents of children with allergic disease," she said. "Too often in my clinic I see allergic children with clinical anxiety (or) depressive symptoms; however, they are receiving no care for these conditions."

"We don't know how treatment for allergic diseases may effect or change the risk for internalizing disorders and we hope to study this in the future," Nanda said.

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