Most people wouldn't think twice about sharing their earbuds, but you may want to think again ... because they are covered in bacteria.
Heidi Mitchell, WSJ health and wellness reporter, says "they are pretty germy. If you think about what's going on in your ear canal, it's a nice, hot humid environment for the bacteria to thrive. Then you stick this thing in there, [and] the bacteria like that." Mitchell said that some bacteria, including MRSA, can live for a week on an inanimate object.
However, she said it's not highly likely because headphones and earbuds aren't very good transmitters. A study in India showed that while there was a highly elevated number of bacteria in chronic earbuds users, but there wasn't a higher risk of infections.
To keep earbuds clean as they are tossed in gym bags, use isopropyl wipes to occasionally disinfect them, especially after use in the gym.
The situation isn't really any better with larger over-the-ear headphones as catching lice may be a possibility.