More airports are using back-scatter scanners like this one at O'Hare International Airport in Chicago. Scott Olson/Getty Images hide caption

itoggle caption Scott Olson/Getty Images

In the study, people who washed their hands after making a tough choice seemed less worried about it. iStockphoto.com hide caption

itoggle caption iStockphoto.com

Someone who looks like this could be in your family tree. Chip Clark/Courtesy of the Smithsonian Institution hide caption

itoggle caption Chip Clark/Courtesy of the Smithsonian Institution