If it seems like everyone around you is constantly sneezing and sniffling, it might be because allergies are on the rise. As New Scientist reports, several studies seem to indicate this is an ongoing trend. While allergies were rare before the mid-20th century, they’re now a common occurrence in children and adults alike. According to the Food Allergy Research and Education Organization, 15 million people in the U.S. have a food allergy.

To make matters worse, some of the fastest-developing countries are seeing a steady increase in allergies, especially in China. Asthma rates among children in Shanghai rose from 2 percent to 10 percent between 1990 and 2011.

So what exactly is at play here? Scientists think the rise in allergies has much to do with how drastically our lifestyles have changed in the last century. In particular, many modern people spend most of their days—and lives—indoors, which wasn’t always the norm. Spending time outdoors at an early age helps expose you to certain microbes “that have helped hone the human immune system for millennia,” New Scientist notes.

For that reason, children who grow up on farms are less likely to develop allergies. However, scientists still don’t understand exactly how these microbes help prevent our immune system from producing Immunoglobulin E, which is released in response to an allergen coming into contact with the body.

Fortunately, there are ways to keep your allergies under control, even if you can't prevent them entirely. Showering before you sleep, using an air purifier, and keeping pets off your bed are just a few of the quick tips you can try.

[h/t New Scientist]