If you’ve never gotten sneezy around a cat, phlegmy around pollen, or had to run the other way when someone served shellfish for dinner, those of us elbow-deep in Flonase and Benadryl salute you. But we’ve also got a warning: you’re not in the clear yet. Although people who don’t suffer from allergies are actually in the majority — experts estimate that up to 30 percent of adults and 40 percent of children in the U.S. have allergies and only 3.6 percent of Americans have food allergies or intolerances — there’s still a chance they’ll get them at some point.

Adult-onset allergies, seriously? Seriously. Immunologist Kanao Otsu explains it to New York magazine’s Science of Us like this: there are two basic time periods during which you can develop allergies. Either the elementary school years or early adulthood (starting around 18 years old or so). Developing new allergies any later than that is rarer, but occasionally happens too.

Not all allergies you start experiencing as an adult are really adult-onset allergies, though — for example, it’s possible you’ve actually had seasonal allergies all along, but they’ve gone from dormant to active because of changes like moving to a more humid or polluted area. But if you’ve been truly allergy-free up until you started adulting, all that time spent at your computer and Netflixing might be to blame. As adults, we often have less exposure to the stuff we were around all the time when we were running around outdoors — think grass, pollen, and mold. When our immune system stop coming in contact with those allergens regularly, it might start to think they’re foreign or toxic agents, allergy and immunology doctor Feryal Hajee explains to Science of Us.

That explains seasonal allergies, but what’s with feeling ill every time you have ice cream? Blame lactase, an enzyme that helps the small intestine digest lactose, the sugar in milk. Most of us are born with it, but as we get older, our lactase levels start declining. Translation? All that lactose we consume goes to your colon without being digested. And once it’s there, bacteria break down the sugars, causing gas, nausea, and bloating.

Not everyone is equally afflicted — some ethnic groups, like people of East Asian, West African, Arab, Jewish, Greek, and Italian descent, are more likely to develop lactose intolerance. And some illnesses, like Crohn’s, can cause it too. But if you think you’re one of the unlucky few who can’t eat their weight in Cherry Garcia, think again. An estimated 65 percent of the global population has a reduced ability to digest lactose.

Don’t worry, there’s a silver lining… at least according to some scientists, who believe that total avoidance of lactose products isn’t the answer. Instead, they recommend a diet that includes small portions of lactose products, so that your body had can get used to breaking it down. Bring on the cheese (in small, restrained portions)!

Diana Vilibert is a freelance writer and copywriter living in Brooklyn, NY. She loves flea markets, martinis, to-do lists, traveling, and wearing leggings as pants. You can see more of her writing at www.dianavilibert.com and follow her on Twitter at @dianavilibert.