6. How long am I contagious when I have the flu or a cold?

As long as you have symptoms. Your ability to spread these viruses remains until the last sniffle, says Bill Schaffner, MD, a physician and infectious disease expert at Vanderbilt Medical Center in Nashville. And you're contagious 24 hours before you first show symptoms. .

7. Is it true that 48 hours after starting antibiotics I can't infect someone else?

Yes, in most cases, and provided you really had a bacterial infection, like strep throat, and not a viral one—against which antibiotics are useless, says Schaffner. But the bug may come back if you quit the drugs early; also, if you fail to complete the full prescription, the leftover bacteria could develop antibiotic resistance and the drugs might not work next time.

8. Is bird flu still a danger?

Yes. As of this writing, influenza A virus subtype H5N1—bird flu—has not made an appearance in the United States. But it still lurks in many parts of the world, particularly Asia and parts of Africa. What makes the virus so scary is its deadliness—it kills 50 to 80 percent of the people it infects. Currently, the virus is primarily passed from an infected bird to a human. "You're not going to get it because you're on the plane with someone who has it," says Richard V. Lee, MD, a physician and infectious disease expert at the State University of New York at Buffalo. Nor does cooked chicken pose a risk, since heat kills the virus. But influenza viruses can evolve rapidly, and despite some promising vaccine developments, if the H5N1 virus develops an ability to spread rapidly between people anytime soon, it could spell disaster.

9. How often do I really need to have my teeth professionally cleaned?

The answer depends on your habits at home, says periodontist Sally Cram, consumer adviser for the American Dental Association. Studies show it takes about three months for bacteria to take hold in the gums. Daily flossers who brush twice a day can get by with twice a year professional cleanings, but those who let things slide or have prior gum disease may need visits every two or three months. Diabetes, autoimmune diseases, and medications like antidepressants that dry out your mouth can also speed bacterial buildup and create a need for more cleanings, says Cram.

10. Do the plastic bags from my dry cleaner contain toxic chemicals?

The plastic bag isn't dangerous, but the chemical residues it traps in your clothing might be, says Sarah Janssen, MD, an expert with the Natural Resources Defense Council, an environmental advocacy group. That smell your dry-cleaned clothes give off is perchloroethylene (perc), a chemical the state of California classifies as a potential carcinogen. Reduce your exposure by removing the bag and hanging the clothes outside—or in your bathroom with the window open or the fan on—to air. Don't leave bagged clothes in a hot car: The heat accelerates perc's release, and could make the air in your car toxic, says Janssen.

11. Are the new birth control pills that eliminate your periods really safe?

Yes. There's no evidence that suppressing your period is dangerous. The periods you get on the regular Pill aren't real anyway, because the hormones prevent your uterus from building up the thick lining that's normally shed during menstruation. One reason the Pill's inventors included the off week was to mimic the normal menstrual cycle in the hope that the Pope might bless the Pill. Needless to say, he didn't.

12. Will staring at a computer all day make me blind?

No. A marathon computer session is like a long hike. "If you walk long enough, your legs will be tired, but that doesn't mean you've permanently damaged them," says ophthalmologist John C. Hagan III, MD, a spokesperson for the American Academy of Ophthalmology. Focusing on a computer screen—a fixed distance—will leave your eye muscles tired and stiff, he says, plus you tend to blink less. The antidote: Look up from the computer screen every so often and focus on something 20 or more feet away, then blink briskly four or five times. .

13. Can diet soda kill me?

If you mean, could it give you cancer, the answer is probably not. Diabetes? Unlikely. Osteoporosis? Maybe. And it seems possible that the drinks are related to weight gain.