A sore throat.
No need for smoking. I'm sure Britney is rich enough to get her hands on some sort of virus she could apply to her throat right before recording. She would achieve the raspy quality without all the wheezing and pesky lung cancer. Win-win.
I sound like a diner waitress right now. "What'll you have, sweetheart?" I began my day with an incredible man voice and it has progressed now to the point where I'm quite certain I could sing along with Tracy Chapman and NOT do high harmony. Feel free to be impressed. I am.
And I was fortunate enough to obtain my throat virus free of charge. I am so frugal.