Many people with sleep apnea wear a CPAP machine mask in bed to help them breathe. Amy Walters/iStockphoto.com hide caption

itoggle caption Amy Walters/iStockphoto.com

Keratoconus is an eye condition in which the normally round cornea thins, causing a cone-like bulge to develop. Courtesy of JirehDesign.com hide caption

itoggle caption Courtesy of JirehDesign.com

Peggy O'Brien-Murphy receives a massage from therapist Loretta Lanz. O'Brien-Murphy was among the participants in a study that found both relaxation and deep tissue massage are effective treatments for lower back pain. /Group Health Research Institute hide caption

itoggle caption /Group Health Research Institute

Artificial hips have been a big advancement in treating debilitating arthritis. But there have been reports of medical issues — some serious — in patients with all-metal implants. iStockphoto.com hide caption

itoggle caption iStockphoto.com

A tattoo artist prepares inks before working on a client. The FDA says it wants to learn more about what goes into tattoo inks. Maggie Starbard/NPR hide caption

itoggle caption Maggie Starbard/NPR

Most Americans spend the majority of their waking hours sitting still in front of a computer or television. iStockphoto.com hide caption

itoggle caption iStockphoto.com

Paul Rider runs on Mulholland Drive in Los Angeles, March 25, 2011. Researchers say a moderate running regimen is actually beneficial for the joints of people with healthy knees. Dennis J. Provost for NPR hide caption

itoggle caption Dennis J. Provost for NPR