A fresh excuse not to wash your hair

Greasy hair may not help you to attract the object of your affection, but it might reduce the amount of ozone you breathe in.

Lakshmi Pandrangi and Glenn Morrison from the University of Missouri in Rolla exposed eight washed and eight unwashed hair samples to ozone for 24 hours. They found that, on average, unwashed hair absorbs around seven times as much ozone as freshly washed hair.

Ground-level ozone can cause respiratory problems and has been associated with increased mortality. Morrison says that having greasy hair could reduce your ozone exposure if you are indoors. "For dirty hair, the ozone concentration around the head is likely to be substantially lower than the level in the room," he says.

Nodding off can help you remember

Is it time to dream up a fresh theory of sleep? We're all familiar with the concept of a power nap, but it could be the very process of falling asleep that's beneficial to the brain. Perhaps sleep itself is a mere side effect.

"A nap of just 10 minutes can reduce drowsiness, even though most models of sleep suggest you need more time to see an effect," says Derk-Jan Dijk at the University of Surrey, U.K. "It's an anomaly -- there is a discrepancy between how much sleep we think we need and the data."

Olaf Lahl at the University of Dusseldorf, Germany, has shown that simply falling asleep does more than refresh the brain -- it can also improve recall. Lahl's team asked students to memorize a list of words and tested their ability to recall the list after an hour of playing solitaire. Some of them were allowed a five-minute catnap at the start. The catnapping students recalled significantly more words than the students who were constantly awake.

Teens turn deaf ear to hearing loss

Teenagers seem to know that loud music can damage their hearing, yet most see no reason to lower the volume on their iPods, a small study suggests. In focus-group discussions with students at two high schools in the Netherlands, researchers found that the teens were generally aware that blasting an MP3 player could harm their hearing.

Yet most said they usually played their own device at maximum volume and had no plans to change that.

Big belly raises Alzheimer's risk

Having a big belly in middle age appears to greatly increase one's risk of developing Alzheimer's disease or another form of dementia decades later, researchers reported.

Their study tracked 6,583 people in northern California for an average of 36 years starting when they were ages 40 to 45. Their abdominal size was measured at the outset of the study.

Heparin recalled in three countries

Supplies of the blood-thinning drug heparin are being recalled in France, Italy and Denmark because they are contaminated or suspected of being contaminated, although there have been no reports of patients being harmed by the medicine in those countries, the Wall Street Journal said.

The European Medicines Agency presumes the contaminant in all three countries is the same as the one identified in recalled U.S. batches of the drug, a chemical called over-sulfated chondroitin sulfate, the article on the Journal's Web site said.

AIDS vaccine effort gets an overhaul

The U.S. government began a major overhaul of its effort to produce an AIDS vaccine, stressing a return to basic scientific research after the failure of a key clinical trial last year.

Government officials at a summit with AIDS scientists pledged to prioritize spending on lab work and animal tests rather than expensive, and thus far disappointing, large-scale vaccine trials on humans.