Contrary to popular belief, anyone can develop new allergies to certain foods, environmental factors or other triggers, for a variety of reasons, according to an allergist from the global health system Cleveland Clinic.
“Allergies can ebb and flow throughout life, and adults who’ve never had an allergy can suddenly find themselves having an allergic reaction to a trigger that previously didn’t bother them or vice versa,” says Lily C. Pien, MD, MHPE.
Dr Pien explains that allergies are the result of the body mistaking a harmless substance, such as a type of food, pollen, animal dander or dust mites, for a dangerous intruder and consequently mounting a defence. The body releases a chemical called histamine in reaction to this trigger, or allergen, which causes symptoms of an allergic reaction.
“Depending on the allergen, you may experience symptoms including hives, itchiness, a rash, runny nose and scratchy throat, swelling, trouble breathing, and vomiting,” she adds.
However, the reason why people develop allergies remains a topic of debate in the medical world, according to Dr Pien. “Allergies are a product of both nature and nurture. We know that our genetics can predispose some of us to have an allergy. Exposure to the allergen can turn on allergic antibody production,” she explains.
“At some point, for some people, re-exposure to the allergen causes clinical allergic symptoms related to the previous allergic antibody production. However, the reasons why the clinical symptoms get turned on, when they’ll turn on and for whom, are still not well known at this point.”
Adult food allergies
Discussing food allergies, Dr Pien says one reason these can appear later in life is related to other allergies the individual may already have. “We find that allergies to shrimp are sometimes coupled with a dust mite allergy,” Dr Pien says. “Some people will already know they have an allergic reaction to dust. Then over time, they find they can’t eat shrimp without a reaction. We don’t know how these allergies might be related if there is cross-reactivity, or coincidence involved.”
Dr Pien says the same is true for people with allergies to airborne allergens like pollen. “A ragweed allergy, for example, can be coupled with oral allergy symptoms to bananas, watermelon and cantaloupe. That’s because, at the molecular level, there are similarities in the substances found in these pairings. Your body sees them as similar invaders and mounts a defence against them.”
At other times, says Dr Pien, food allergies in adults may be a matter of long-term exposure. “We see adults who never noticed a reaction to a food may suddenly find that their lips swell after eating it. Perhaps they were genetically predisposed to the allergy all along, but it took years of exposure to trigger that response in their immune system.”
Dr Pien says food preparation can also play a role, for example, some people who have pollen-fruit syndrome find that they can eat baked apples, but get an oral rash or itchy mouth after eating raw apples, especially if they are not peeled.
Food allergies can also come on after a period of intermittent exposure. “If you eat a food relatively consistently, your body can build up a tolerance to that food, even if you’re technically allergic to it. Stop eating the food for some time and that tolerance can fade. The next time you eat it, it can result in an allergic reaction. In such a case, the allergy was there all along, without you even knowing it,” Dr Pien says.
Seasonal and pet allergies
Dr Pien says new allergic reactions to outdoor allergens can happen after moving to a new region, exposing people to a new ecosystem. Another explanation is related to changes in medications taken, or specifically if a person stops taking the medication. “Some people might take antihistamines without realizing it — for example, it can sometimes be present in medication prescribed for insomnia — then stop taking it or change to a new medication and suddenly feel the effects of seasonal allergies,” she says.
Similarly, pet allergy symptoms can develop in adults for a variety of reasons, says Dr Pien. It could be that a new dog sheds more than others the individual lived with previously, or a new cat is male yet the person grew up with female cats. Or a person could be spending more time with their pets now than they did previously.
Dr Pien stresses that allergies can be serious and even life-threatening, so if individuals suspect they have an allergy, they should talk with a healthcare provider before attempting to diagnose or treat themselves. She adds, “A healthcare provider will be able to help you identify any allergies you have and discuss approaches to managing them. New allergies may take three to five years to develop, so if you haven’t had an allergy test recently, they may want to perform one.”
