The crotch is not cotton
Ideally, the whole kit and caboodle will be woven from these natural fibers, but at the very least, the center stretch should be lined in cotton to keep your nether region fresh and dry. Synthetic fabrics—like polyester and lace—can trap heat and moisture, irritating the skin and creating an environment for bacteria or fungus to overgrow and multiply. Silk (sorry) has the same effect. Save the fancy for special occasions, but otherwise stick with cotton—the fabric is light and breathable and can help reduce your risk of yeast infections, urinary tract infections, and other less-than-pleasant issues. (Related: Here are 13 things your vagina secretly wants you to know.)
The size is too small
Muffin top: that might be reason enough to make sure your skivvies fit well. And if you can, try before you buy: “There isn’t a universal sizing system for brands,” Miriam Hernandez, an intimate apparel stylist and designer, told TotalBeauty.com. “I’ve seen mediums that fit like extra smalls.” So if you need to go up a size, do it in the name of unwanted pinches, panty lines and bulges—and perhaps even more importantly, for your vaginal health. Tight-fitting undergarments (and pantyhose for that matter) can keep you lady bits hot and sweaty—and not in the good way you’re thinking, but more along the irritation- and infection-promoting lines. And about your man’s parts in his tighty-whities: wearing briefs may up his chances of getting jock itch, but they won’t mess with his sperm counts (myth!). Read more about these other myths about infertility.