You may have to pump yourself full of Zyrtec just to step outside during allergy season because your ancestors couldn't keep their hands off those sexy Neanderthals, suggests two new studies in the American Journal of Human Genetics.

Neanderthals and a second now-extinct hominid—Denisovans—were living in Europe and Asia for hundreds of thousands of years before humans arrived and were likely well-adapted to the local pathogens, according to a press release.

When humans showed up and started interbreeding, they took on some of the Neanderthal and Denisovan genes. One of the studies reports three genes having to do with "innate immunity" in modern humans show more similarities to Neanderthal and Denisovan genomes than the rest.

Innate immunity is the body's first response to pathogens and other foreign substances, NPR reports. The three genes from Neanderthals and Denisovans "are key components of innate immunity and provide an important first line of immune defense against bacteria, fungi, and parasites," according to the second study.

But there's a "trade-off," as researcher Janet Kelso puts it. "I suppose that some of us can blame Neanderthals for our susceptibility to common allergies, like hay fever," she tells NPR.

That's because these genes that helped ancient humans ward off disease in a new world can cause the body to overreact to minor foreign substances, such as pollen, according to the press release.

(A thigh bone revealed the timing of human-Neanderthal sex.)

This article originally appeared on Newser: Sex With Neanderthals May Explain Modern Allergies

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