Wearing underwear underneath your shapewear is up to you. But with shapewear styes that are designed for maximum compression and smooth lines, undergarments may get in the way of the overall look and feel. "I will say that when I created Spanx 20 years ago, I designed them...so you don’t wear underwear under them," Spanx founder Sara Blakely told TLC. “Half the women wear underwear under it, and so that’s fine, too."