Not only can constant exposure to loud music cause hearing loss, but you also need to be concerned with the earbuds themselves. It has been shown that in-ear headphones increases bacteria growth inside the ear. Most people do not take the time to disinfect their earbuds before and after using them. Bacteria can easily be transferred from your hands to your earbuds and, in turn, promote growth in your ear. And to think people actually share their earbuds with others! This puts you at a much higher risk of developing an ear infection. My advice is to keep your earbuds to yourself and make sure you are disenfecting them, along with washing your hands, regularly.
Another concern, however, is using earbuds when you are working out. Not only are you handling things inside the gym, handling your headphones, and then sticking them in your ear, but you are also sweating. Excess sweat buildup in the ear, along with using in-ear headphones, can lead to swimmers ear. The combination of the two can cause a breakdown of the skin inside the ear, allowing for bacteria to enter and infection to occur.
I’m not saying to stop using an ipod altogether, I just want you to be cognizant of what may be going on and to make sure to keep your earbuds clean as a way of prevention. If nothing else, switch them out every so often.