Bunions
A Bunion is a deformation of the bones and joint at the base of your big toe. You might notice your toe becoming slightly crooked, and even start turning in towards your other toes. Though bunions are a common thing, they can get extremely irritated and uncomfortable during activities involving lots of leg work. (i.e. jogging, hiking, biking. etc.)
Causes
Bunions are caused by abnormality affecting the ligaments and tendons of the foot. (If you are standing up, try to point your toes to the sky. That big vein-like ligament you see coming from the bottom of your leg and going into the top your foot is the one we're talking about!)
The abnormality itself can be caused from a variety of things such as flat feet, genetic bone structure, or excessive stretching of the ligament itself (common problem with dancers.)
note: Though doctors don't necessarily believe that bad footwear is a cause of the problem, it is quite clear that it will make the problem worse.
Treatment
Treatment for bunions is a little different than most, being that it doesn't actually help fix or correct the problem at all; just makes it easier to cope with. If you have shoes that irritate it, you will probably want better fitting shoes, or some thick socks to reduce chaffing and put more padding between your bunion and the shoe. If it's already irritated you can use ice and ibuprofen. If the discomfort is extreme or intolerable, there are surgeries to permanently correct this issue.