Patients with asthma and hay fever have an increased risk of developing psychiatric disorders, finds a new study published in open-access journal Frontiers in Psychiatry. Almost 11% of patients with common allergic diseases developed a psychiatric disorder within a 15-year period, compared to only 6.7% of those without – a 1.66-fold increased risk. While previous studies have linked allergies with certain psychiatric or emotional disorders, this is the first to find a connection between common allergies and the overall risk of developing psychiatric disorders. The findings could have implications for how doctors care for and monitor patients with allergic diseases.

Asthma, allergic rhinitis (hay fever) and atopic dermatitis (eczema), are among some of the most common allergic diseases and are nicknamed the three “A”s. Dr. Nian-Sheng Tzeng , from Tri-Service General Hospital in Taiwan and lead author of the study, noticed something unexpected about these patients.

“As a clinician, I observed that some patients with the three ‘A’s appeared to suffer emotionally,” says Tzeng. “Therefore, I wanted to clarify whether these allergic diseases are associated with psychiatric disorders.”

When Tzeng and colleagues searched the literature, they found that previous studies had reported links between allergic diseases and specific psychiatric disorders or emotional problems. For example, a study in Denmark found that children with allergic diseases had more emotional and behavioral problems.

However, not all previous research supported this positive link, with one study in Taiwan suggesting that allergic rhinitis is less common among patients with schizophrenia, for example. Clearly, more extensive research was needed for a more complete picture.

Despite the previous research, no-one had studied the link between the three “A”s and the overall risk of developing psychiatric disorders. To study this in a large sample of people, the researchers used an extensive database of health insurance claims in Taiwan, covering a 15-year period.

The researchers identified 46,647 people in the database with allergic diseases and 139,941 without. Unlike previous studies, the researchers included patients of all ages. They found that over the 15-year period, 10.8% of people with allergic diseases developed a psychiatric disorder, compared with 6.7% of those with no allergic disease. This translated to a 1.66-fold increased risk of developing psychiatric disorders for people with an allergic disease.

A closer look at the data revealed that people with atopic dermatitis had a lower risk of developing a psychiatric disorder, while those with asthma and allergic rhinitis had a higher risk. Interestingly, the team discovered that using certain asthma medications was associated with a lower risk of psychiatric disorders in asthma patients.

So, why might patients with certain allergic diseases have a higher risk of psychiatric disorders? Recent research suggests that inflammation is linked to psychiatric disorders, such as depression and anxiety disorders. As allergies also involve inflammation, it is possible that it may contribute to psychiatric disorders in the same patients. The psychological stress of a psychiatric disorder might also contribute to physical symptoms.

The current study did not examine the potential cause of this phenomenon and researchers need to complete further studies to identify the precise mechanisms involved. However, knowing that there is a link between allergic diseases and psychiatric disorders could help doctors to care for their patients.

“We would like to let clinicians who care for patients with allergic diseases know that their risk for psychiatric diseases may be higher,” says Tzeng. “Assessing their emotional condition and monitoring their mental health could help to avoid later psychiatric problems.”