Experts have said allergies like hay fever could cause mental health issues by interfering with feel-good hormones in the body.
Mounting evidence suggests people who have allergies are more likely to have anxiety or show similar behaviours.
According to doctors, distress caused by being sick could raise the stress hormone cortisol, which in turn tampers with serotonin – a hormone responsible for mood.
And the experience of straining to breathe, wheezing, or feeling itchy could simply make people feel anxious.
Dr Ahmad Sedaghat, a professor at the University of Cincinnati, called the body’s reaction to allergies ‘sickness behaviour’, and is a way of keeping a person indoors to recover.
And while allergic reactions cause inflammation as an immune response, the internal swelling has also been linked to conditions like depression.
Dr Sedaghat told The Atlantic: ‘Evolutionarily, all animals have this reaction, called “sickness behaviour”, when they’re sick. It’s meant to conserve energy.
‘The problem is if you have persistent inflammation of the sinuses, what happens over time is that the inflammation essentially builds on itself, making the anxiety and depression worse, which makes it easier for the inflammation to cause more anxiety and depression, and you fall into a vicious cycle where you can’t break out.’
Another biological explanation is that inflammatory chemicals in the sinuses leak into the blood and reach the brain and nervous system.
Dr Sandro Galea, from the Boston University School of Public Health, said: ‘There is good circumstantial evidence that’s growing that a number of mental illnesses are associated with immune dysfunction.’
Maya Nanda, a paediatric allergist at Children’s Mercy in Kansas City, Missouri, said it’s not clear how cortisol alters serotonin, but it could inhibit the production of it or make it fail to bind with its receptors properly.
She told The Atlantic that she first started noticing her patients had high rates of poor mental health a few years ago.
Her patients would appear anxious when discussing their allergies, and in one instance, a child’s asthma in fact turned out to be panic attacks.
Ms Nanda and colleagues conducted a study on a group of seven-year-olds in 2016, published in the journal Pediatrics, which confirmed their concerns,
Children with symptoms like a runny nose and wheezing, caused by an allergy, at age four, were at increased risk of anxiety and depression by the age of seven.
The risk for children with hay fever was three-fold.
Researchers at Columbia University’s Mailman School of Public Health concluded children with a food allergy had a ‘significantly higher prevalence of childhood anxiety’, publishing the results of a study on 80 children in Pediatrics in 2017.
Other studies have even shown that during times of high pollen count, suicide risk increases in women.
The number of people in the world with allergies could be high as 40 per cent, according to The World Allergy Organisation (WAO).
The UK has some of the highest prevalence rates of allergic conditions in the world, with over 20 per cent of the population affected.
Allergy UK state that up to 57 per cent of adults and 88 per cent of children with hay fever have sleep problems, leading to daytime fatigue and decreased cognitive functioning.