There are pecs and then there are boobs. And it turns out, up to 50% of men in the U.S. have the latter, according to a review from the Cleveland Clinic Journal of Medicine. And FYI, the condition’s called gynecomastia.

But don’t buy stock in the bro (thanks, Kramer!) just yet. Assuming you aren’t born with a genetic disorder like Klinefelter syndrome that can cause the condition, bra-ready jugs are pretty simple to avoid if you heed the causes. Breast tissue—which both women and men possess—feeds off of estrogen hormones. While women naturally have more estrogen, and men naturally have more androgen hormones, men can easily get their estrogens-to-androgens ratio out of whack. The result: sprouting boobs faster than your high school’s head cheerleader.

Here, the nine sneakiest cup-fillers: