In a new, large-scale study, eczema, hay fever, and asthma are linked to an increased risk of developing mental illnesses. The study backs up previous work and may help to guide clinicians as they treat these people.
As someone who has all three of these, I was particularly interested to see the results. But I must also admit that I felt slightly unnerved.
I've had asthma and eczema since I was a baby, and I developed hay fever in my late teens. I've also had a few run-ins with mental health over the years, but I would never have thought that they could be related.
Looking for unexpected links
At first glance, it seems unlikely that allergies and mental health would be linked in any way; itchy skin, a runny nose, and a wheezy chest don't seem to be particularly aligned with emotional and cognitive challenges.
Lead study author Dr. Nian-Sheng Tzeng — from Tri-Service General Hospital in Taiwan — explains why he decided to look for associations.
"As a clinician, I observed that some patients with the three A's appeared to suffer emotionally. Therefore, I wanted to clarify whether these allergic diseases are associated with psychiatric disorders."
When Dr. Tzeng and his team started to peruse the scientific literature, they found that some previous studies had actually found clues that there might be a relationship.
For instance, a Danish study concluded, "Children with eczema, asthma, or hay fever had more emotional, conduct, and hyperactivity problems."
However, overall, results from previous studies were contradictory, and no firm conclusions have been drawn. There was also a notable gap: nobody had looked specifically looked at the link between the three A's and the risk of psychiatric disorders.
Dr. Tzeng and his team were intrigued; they had found a gap in current understanding and set out to fill it. To do so, they took data from the Taiwan National Health Insurance Program. Across 15 years, they followed people of all ages.
In total, the study involved 46,647 people with allergic diseases and 139,941 without.
Allergy increases psychiatric risk
Dr. Tzeng's suspicions were confirmed: across the duration of the study, 6.7 percent of participants without allergic conditions developed a psychiatric condition. For those with an allergic condition, this figure rose to 10.8 percent. That's a worrying 66 percent increase.
Of the three A's, eczema produced the smallest increase in risk. The researchers also showed that the use of certain asthma medications lowered the risk of developing a psychiatric disorder.
The next question that comes to mind is, "What mechanism is behind this connection?" Over recent years, there has been a great deal of interest in inflammation and its role in mental health — particularly depression and anxiety.
If someone has inflammation on their skin caused by an allergy, it might also be present in the brain. On the other side of the coin, it's possible that the stress of an allergic condition worsens psychiatric symptoms that already exist. The relationship is likely to be a complex two-way street.
The psychology of itching
I know from personal experience that being anxious increases how much I scratch my skin (in fact, I'm on a tight deadline now and have been scratching intently). And, vice versa — scratching my skin until it is sore increases my levels of anxiety. It can be a vicious cycle.
Beyond personal experience, scientists have shown that the psychology of itching is a convoluted topic. One author, writing about eczema and pruritus — or severe itching, a symptom of many conditions, including all three A's — says:
"[I]tch can be induced simply by thinking about it. In pruritic skin diseases, [...] the severity of the diseases do not adequately account for the intensity of itch reported by patients, and psychological factors have often been attributed to being responsible for the perception of pruritus."
Although the current study cannot demonstrate exactly why this relationship exists, it adds to the evidence that there is some kind of interaction between allergic and psychiatric conditions. The researchers hope that the findings might inform clinicians about these potential risks.
"We would like to let clinicians who care for patients with allergic diseases know that their risk for psychiatric diseases may be higher."
Dr. Nian-Sheng Tzeng
"Assessing their emotional condition and monitoring their mental health could help to avoid later psychiatric problems," adds Dr. Tzeng.
People with any or all of the three A's might find these results concerning. However, for me, they bring a certain relief. They provide a potential explanation for my lifelong dalliance with borderline depression and anxiety. In a way, it helps explain these mysterious negative emotions that visit me intermittently.
Also, this work provides further evidence of the link between psychiatric health and inflammation. Potentially, this could lead to novel ways to treat mental health issues.