I'm 40 and a smoker. My feet have been numb for at least 2 weeks. What could be the cause?

There are many things that can cause this some are very serious like diabetes some not so much like proper foot ware. I would look at diet check your feet for swelling and think about what you ware on your feet. If you can't figure it out then see a doc if its diabetes you could be in real trouble if you don't get it taken care of. Goodluck.

I am not a doctor. But, I would see a doctor. I smoked for 29 years, and now thanks to Chantix, have not smoked for the last 6 years!
I don't think smoking would cause your feet to be numb. Poor circulation might cause it. I would see a doctor. If you can't afford one, there might be a free clinic in your area. I do know that VA has free clinics, one close to me. Good luck.