If you've been smoking for a while, you may be used to seeing yellow tobacco stains on your fingers. The yellow discoloration that occurs on your fingernails is something a little different. Some of the yellow may be coming from cigarette smoke wafting up your fingers from the ciggy in your hand. There's a more ominous cause, though. That yellow tint you see on your nails after months, years or even decades of smoking is the effect of reduced blood flow from inhaling cigarette smoke. The color is unsightly, but it's also an indication that your nails aren't receiving proper nutrition, which leaves them vulnerable to fungal infection.