Brain cells.

I was talking to my friend on my cell while it was charging. she says that can cause brain cancer. now I'm seared!

Hello! Cell phones emit the same small amount whether plugged in or not. People who regularly use cell phones don't have higher cancer rates, says the National Cancer Institute. Just to be safe, the FDA has these recommendations: 1) Make conversations short, and 2) use a headset so there's more distance between the antenna and your head. But, bottom line, billions of people safely use mobile phones.

I sleep without underwear or a bra. Is this OK for my body? It is weird to sleep naked?

Feel free to go commando! It's fine to forgo panties once in a while. Without air, girls' privates can get infections since yeast grows in warm, dark, moist areas, explains Joanne Serra, R.N., clinical coordinator at Fair Lawn Women's Health Group, New Jersey. As for a bra, it doesn't matter--whatever you find comfortable. And it's not weird to sleep naked. One in 10 people bed-bares it.

Why can some girls eat all they Want and never gain a pound?

Those skinny girls who go for seconds at the all-you-can-eat buffet have faster metabolisms (their bodies burn calories at a higher rate). As unfair as it may seem. there's nothing you can do to get a metabolism upgrade, explains Cynthia Sass, R.D., spokesperson for the American Dietetic Association. So focus on taking great care of your body. Choose healthful foods most of the time, and splurge only occasionally. And, no need to be a workout queen--just walk, dance or move around for 30 minutes most days.

I've sucked my thumb since I was a baby, and I can't stop. It's making my teeth crooked. Help!

You're not a bad person for finding comfort in thumb-sucking, but you are permanently damaging your choppers. The upper teeth will begin to protrude forward while the lowers draw inward, explains Dr. Sabine Hack, adolescent psychiatrist and assistant professor of psychology, New York University Medical Center. Look for other ways to soothe yourself--reading, taking long baths or talking on the phone. You can also put icky-tasting polish on your nails (Mavala Stop, $7, amazon.com), or wear cotton gloves to bed. A therapist can help you beat this habit for good.

Stumper of your own? Send your question to Body Q&A, Girls" Life, 4517 Harford Road, Baltimore, MD 21214, or e-mail it to [e-mail].

FACT OR FICTION?

I've heard you can go deaf from cranking up the headphones on your iPod.

FACT! Rockin' out to your iPod may be great for your parents' sanity, but, according to recent studies, hearing loss is directly linked to teens pumping up the music, And if you love to max out your MP3s, it's not just hearing loss you have to worry about. So, how can you get your Coldplay fix without going cold turkey? Experts say one hour on a portable player at 60-percent of the volume is relatively safe.