While the 32-year-old princess of pop has been the object of America's affection since "Baby One More Time" debuted in 1999, Spears explained that even she feels insecure about her image sometimes.
"I think it's important to look good and feel good about yourself, but I go both ways on it. I think it's cruel how the world puts so much emphasis on our looks," she said, confessing that she's altered her body a few times.
"A doctor I see, Dr. Kanodia, does fun stuff to me sometimes -- I've had lip injections before. He has this peptide-based face-care product; it's green and slimy, and you mix it together and put it on your face. It does wonders. You leave it on overnight," she said. "Can you tell I love skin care?"
Spears went on to say that "in this business you make a deal with the devil" when it comes to looks, but admitted that she's "learned you kind of have to go with it.
"What I do calls for me to look good. People expect that. I kind of take it as my job," she explains.
The "Work Bitch" singer was reminded of how bad media scrutiny can be while watching an episode of Keeping Up With The Kardashians.
"I see Kim and what she went through when she was pregnant -- the tabloids were so mean to her because she was big. At one point in the show she was upset and said something like, 'I would be lying if I said that the criticism from the paparazzi while I've been pregnant hasn't taken a toll on me.' And I was like, 'Bless her heart,' because I remember that time," she said.
"First of all," Spears continues, "you are already emotional, and then the paparazzi are taking pictures of you pregnant. That should be the time when your body is the most treasured. I loved being pregnant for so many reasons, not to mention the sex is awesome then."
The January 2014 issue of InStyle hits newsstands on Dec. 13.