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Why Do You Have Allergies All of a Sudden?

By Camille Peri
WebMD Feature
Reviewed by Luqman Seidu, MD

If you’ve made it to adulthood without allergies, that’s great. You might not be off the hook, though.

You don't have to be a child to have a first bout of hay fever or red, itchy skin. Half of new allergies happen in adults, most often in their early 40s.

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Common culprits for adult-onset allergies include animal dander, pollen, dust mites, and mold. You can get the right treatment once you figure out what's causing you to sneeze, sniffle, or itch.

Is It a New or Old Allergy?

Seemingly out-of-the-blue allergic reactions could be new flares of old allergies. Childhood allergies sometimes fade and then return years later. Or you may have always had an allergy that wasn't diagnosed before. The symptoms may seem new because:

  • You're exposed to the allergen more now than you were as a child.
  • Your immune system became more sensitive to the allergen, so symptoms that were once mild are now strong.
  • Your allergy has evolved. "You can start with a spring allergy to grass or trees that moves to ragweed in fall, and eventually to dust mites or mold," says James Sublett, MD. He's an allergist in Louisville and president-elect of the American College of Allergy, Asthma, and Immunology.

New allergy symptoms can be triggered by:

  • Your job. What’s around you while you work? Common triggers for sinus allergies and asthma on the job include flour and grain, rubber latex, wood dust, and chemicals. Working with soaps, solvents, and greases can cause patches of itchy red skin. Changes in your job duties can also expose you to new allergens or more of them -- for example, if you go from sitting at a desk to inspecting buildings.
  • Moving. Like changes in your work setting, moving to a new city, new neighborhood, or new house can bring on symptoms. These kinds of things can set them off: mold, dust mites, ventilation systems, if the previous owner kept animals indoors, or if the house is near a busy highway (where pollutants may make some allergens more potent). You might not have symptoms right away. It can take 3 to 5 years for your immune system to react to an allergen, says Michael B. Foggs, MD. He's an allergist with the American College of Allergy, Asthma, and Immunology.
  • Oral allergy syndrome. If you have hay fever, you can get an allergic reaction in your mouth from eating certain raw fruits or vegetables or tree nuts. Why? Your immune system recognizes pollen and similar proteins in the food and mounts an allergic response to it. Say you're allergic to birch pollen. After exercising outdoors one day, your mouth may itch when you eat an apple and some almonds. It’s not uncommon for something you have eaten for years to suddenly cause a reaction.
  • Shellfish. Adults are more likely than children to get a shellfish allergy. It’s one of the top food allergies for adults. The reactions are usually brought on by crustaceans like shrimp, lobsters, and crab.

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