Ahh..springtime. That warm breeze, the sun on your face… and lots and lots of plant sex. [sexy music playing] “Let’s take it slow, baby.” Yes, flowers, grass and trees are getting it on, and seasonal allergy sufferers are miserable. That’s because our immune systems mistake harmless grains of pollen for dangerous intruders. They go into overdrive mode, releasing a chemical called histamine that triggers those annoying symptoms. Seasonal allergies are affecting more and more people, and scientists are scrambling to figure out why. One idea that’s gaining traction is the hygiene hypothesis. The theory is that our immune systems needs training when we’re kids to learn how to respond to organisms that cause disease. If the immune system doesn’t get enough exposure to things like bacteria, it might not be able to tell what’s a real threat and what’s harmless. It’s also more likely to misfire and overreact to innocent visitors like pollen. When it does, it releases the histamine that triggers those annoying seasonal allergy symptoms. This is still just a theory… and it doesn’t explain why some people get allergies and others don’t. But it is helping scientists understand some interesting relationships. Like, why kids who grow up on farms or who have more siblings tend to have fewer seasonal allergies. And babies born via c-section tend to have more. The hygiene hypothesis proposes that farms, siblings, and vaginal birth expose kids to the kinds of “good” bacteria that give their immune systems plenty of practice separating friend from foe. Evidence for the hygiene hypothesis also shows up in…other places. Studies analyzing the fecal matter of people with seasonal allergies found that they were missing lots of the “good” bacteria. Which could be why some allergy sufferers say they had fewer symptoms when they added bacteria-rich foods like yogurt to their diets, though scientists say more research is needed to find out why. The hygiene hypothesis might also help explain why kids with higher levels of a chemical called triclosan in their bodies tend to have more seasonal allergies. Triclosan is the active ingredient in most antibacterial soaps, hand gels and wipes. According to the hygiene hypothesis… it’s killing good bacteria along with the bad, which makes kids’ immune systems more likely to mistake pollen or for a serious threat. That’s why it’s probably a good idea for us to stop buying antibacterial products and stick with regular soap and water. Now, the take-home message from these studies isn’t that you should stop cleaning your homes or washing your hands in an attempt to try to keep allergies at bay. The hygiene hypothesis is more of a starting point. A way for us to start thinking about how our modern environment might be shaping our health.