Here's a cool thing. When you're sick, or allergic, or something flies up your nose, and you spasm and expel mucus, it's polite for anyone around you, including complete strangers, to call attention to it. In English-speaking countries they say "Bless you," in most of Europe they say "Health."
In almost every culture, the polite response is "Thank you." As in "Thank you for calling attention to my embarrassing bodily function." As in "Thank you for making me thank you while I'm probably still dealing with how something inside me is now outside me." As in, "Thank you for alerting me that for the next three months, I'll be having impromptu two-line conversations with strangers, because my body thinks flowers want to kill it."