healthHealth and Medicine

Why Do Some Adults Suddenly Develop Allergies?


Jonathan O'Callaghan

Senior Staff Writer



This year, something rather horrific has happened to me. For years, I have mocked friends and family for suffering from hay fever, while I’ve otherwise been immune. But karma has caught up with me. I, too, am now apparently allergic to pollen.

But why? For a good three decades, I’ve been completely fine. Suddenly, this summer I was struck with runny noses and crying eyes at random moments. And it appears I’m not alone in developing adult-onset allergies.


“Lots of people assume that everyone with hay fever develops it in childhood, but we've had people coming to us in their 70s who've just been diagnosed,” Beverly Adams Groom, chief palynologist at the National Pollen and Aerobiology Unit at the University of Worcester, told the BBC a few years ago.

Allergies like hay fever – also called allergic rhinitis or just seasonal allergies – are the result of our immune systems reacting to something harmless. Our bodies produce allergic antibodies and, when we inhale more allergens, they burst and produce histamines.

These usually protect the body, sneezing away things like bacteria. But if our body mistakes something harmless like pollen for bacteria, then it can produce histamines by mistake. And this can lead to some rather annoying symptoms.

Histamines (3D rendering shown) are to blame for our allergies. Juan Gaertner/Shutterstock

Hay fever, for example, can cause cold-like symptoms like sneezing and a runny nose. While these are usually mild, it can lead to more extreme symptoms like problems sleeping.


Symptoms generally improve over time, and in some cases disappear entirely. While up to 40 percent of children have hay fever, only about 10 to 30 percent of adults have it.

But while it goes away for some, in others allergies can appear to come from nowhere. And it’s not just hay fever. It’s estimated that more than half of Americans with food allergies develop them after the age of 18.

Stephen Tilles, president of the American College of Allergy, Asthma, and Immunology, told Vice that you’re most likely to develop new allergies in your 20s. And if you do develop allergies as an adult, they’ll probably stay with you for life.

Fortunately, if you've reached your 30s without developing allergies, then it's “very unlikely they're going to [do so] later on” said Tilles (although certainly not in all cases). But the bad news is that if you do develop them in a second wave as an adult, they're probably not going anywhere.


“Whereas children may grow out of allergies, especially those to egg, milk and wheat, once an adult develops a food allergy, it usually persists,” noted The Guardian, speaking to Dr Stephen Till, a consultant allergist at Guy’s and St Thomas’ NHS foundation trust.

But the worst thing of all? We don’t know why this happens. While there may be a genetic component to developing allergies, we don’t know what causes them to develop later in life for some.

Moving house could expose you to new substances that you didn't know you were allergic too. Monkey Business Images/Shutterstock

One possibility, specifically regarding food allergies, is due to the globalization of the food industry. Certain foods you might eat in later life such as prawns might be a different species to what you’re used to.

Another possibility is that it’s due to making a major life change like moving somewhere new. This can expose you to new substances that you may have already had an allergic reaction to, you just didn’t know it yet.


“It's also possible that people who haven't moved or encountered a new environment are just manifesting allergies they had when younger, but then went dormant for an oddly longer period of time (perhaps beyond the usual teenage years of hormonal flux) and were only reactivated by some mysterious trigger,” added Vice.

Some sort of shake-up to your immune system could be at play. An infection, illness, or extreme emotional event could result in a sudden allergy in adulthood, although again, the science on that is unclear.

What is clear, though, is that I am now a hay fever sufferer. And it doesn’t look like it is going away any time soon. Great.


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