Celebrities Who Swear by Spanx From mega pop stars to glamorous actresses, many Hollywood A-listers have revealed that they wear Spanx, the not-so-secret, must-have under garment used to smooth away cellulite and hide panty lines. Katy Perry, shown here attending Dream Foundation's 11th Annual Celebration Of Dreams Gala on Nov. 16, 2012, told Us Weekly on Tuesday she felt "fat" without her Spanx: "I almost always wear them." JB Lacroix/WireImage/Getty Images