Big toe right foot, under toe nail theres a yellow line. i haven't been to a doctor in like 20 yrs.i smoke cig.i know my health is bad, but this is new.

I'm : I'm not all that clear on what you mean by a "yellow line." vertical? Horizontal? Perfectly straight? Slowly growing or suddenly appearing? Beyond a better description, adding a link to a photograph would also help. So, given the limit of what information you provided, it's hard to make any kind of reasonable determination as to the cause. I will say that one of the most common causes of discolored toenails is a fungal infection, and while fungal infections of the nails can start with any sort of pattern, it's not typically a "line." i would be remiss in any answer to advise you of the obvious, though. Being a smoker especially, it's probably a good idea to see a doctor every 20 years or so, whether you need to or not, especially if you "know [your] health is bad." as much as it's annoying to see us doctors (believe me, i know!), there is an alternative to bad health..... Good health! if you can post a picture of your toenail, i'll try my best to give you a more meaningful answer.

Many possibilities: Some causes of nail discoloration include trauma due to tight shoes, infection, and medication side effects. Have the feet inspected by a professional to determine the cause of the problem, as treatment varies depending on the diagnosis.