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Adult-Onset Allergies: How They Happen and How to Manage Them

A woman standing in front of trees holds a tissue to her nose

Picture this: You take a bite of your favorite childhood snack — an apple — something your mother used to pack in your lunchbox every day for school. But rather than tasting the usual crispness of a Granny Smith, your mouth instead feels itchy and your throat is scratchy. This could be a sign of Pollen Food Allergy Syndrome, or oral allergy syndrome. Oral allergy syndrome is more common among adults, especially those with a history of seasonal allergies.

Allergies are a response from the body’s immune system, and they are different than food intolerance or sensitivity, which occur when the body has difficulty digesting a particular food or food chemical.

Some patients with allergies may experience what Priya Patel, MD, an assistant professor of Clinical Medicine and associate program director for the Penn Allergy/Immunology Fellowship Program in the Perelman School of Medicine, describes as the “atopic march” — a general progression of various allergic conditions that start early in life. An infant can begin to show signs through atopic dermatitis, also referred to as eczema. Some of these patients may then gradually develop food allergies, then allergic rhinitis (including seasonal allergies) and asthma, explained Patel.

Priya Patel
Priya Patel, MD

An allergy is the immune system’s reaction to foreign substances called allergens. Typically, allergens are harmless. However, when some people are exposed to allergens, their immune system becomes oversensitive and releases chemicals, such as histamine. These chemicals cause the many symptoms of allergies, varying from sneezing, itchy or watery eyes, runny or stuffy nose, to nausea, vomiting, diarrhea, and hives.

Some food allergies, such as milk and egg, are more likely to be outgrown in late childhood compared to others, such as peanut and tree nuts. Drug allergies are also common to outgrow: “80% of people lose their penicillin allergy after about 10 years,” said Patel.

But oral allergy syndrome is one case where new allergies can appear during adolescence and adulthood. The protein structure found in some fruits and vegetables can be similar to the protein structure found in pollen, resulting in cross-reactivity. For example, fruits like melons and oranges can be associated with grass pollen. And apples, cherries, and pears, among other fruits and vegetables, can be associated with birch tree pollen.

“For someone sensitized to birch tree pollen, if they eat an apple, their body will think it’s pollen because of the protein similarities,” said Patel. “However, by the time the food gets to the stomach, it’s now in a warmer environment and the protein can break down. The allergic reaction typically subsides and doesn’t go beyond the mouth.”

Other ways an individual could develop allergies is through genetics — a family history that can predispose someone to allergies — or unfamiliar environmental factors.

Patel described an example of how an individual could live their life without having any pets, thus unaware of any allergies to animals. When they enter young adulthood and live on their own, they decide to get a dog or cat. After living with their new pet for a few years, they may notice frequent watery eyes or nasal congestion. Typically, a few years of exposure to the allergen are needed to develop symptoms of allergic rhinitis.

How to Manage Your Allergies: Scratch Tests and Shots

A person holding a nose spray in their right hand and allergy pills in their left hand

There’s no way to determine if someone will develop a specific allergy later in life, explained Patel. “We know that people who are more atopic — those who have existing allergic conditions — or a history of eczema or asthma, are more likely to develop allergies in adulthood. But we won’t know what those allergies are until they’ve been exposed to them.”

For those concerned about their allergy symptoms and looking for ways to manage them, Patel recommends a three-pronged approach with therapies offered at Penn Allergy and Immunology.

  1. Figure out what you’re allergic to. Keep track of any exposures and the timing of your symptoms. Are your symptoms mostly in the springtime? Do your allergies subside when you’re away from your pets? Penn Medicine offers allergy testing — scratching the skin with small traces of allergens and examining if your body is physically sensitized to them. After knowing your allergies, determine a plan to control your environment and decrease exposure to those allergens.
  2. Optimize medications. Use steroid nose sprays and antihistamine nose sprays to help control inflammation in the nose and reduce congestion. Another option includes allergy pills to alleviate symptoms, along with eye drops to relieve dry, itchy eyes.
  3. Sign up for allergy shots. Your physician can create injections of allergens to slowly teach your body how to tolerate exposures. Using the results from your allergy test, they will add the allergen extract to a vial and dilute it, then inject the most diluted vial into the body. “It’s a slow process, taking roughly 3 to 5 years for your body to grow accustomed to the allergen, but it’s an option for those with chronic allergic rhinitis,” said Patel. “The therapies for treating allergies have really advanced over time. At Penn, we have so much to offer to improve our patients’ quality of life.”


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