Nicotine is a chemical compound found in cigarettes. It is an oily liquid that can combine with water and easily penetrate the skin and nails, leaving them yellow and sallow, according to the National Institute on Drug Abuse. Removing these stains is difficult and can be impossible unless you stop smoking long enough for the discolored skin to shed and be replaced by new skin. If using a lime, squeeze the lime into warm water and mix. If using lime juice, combine it with the water. Dip nail brush into lime solution. Sprinkle sugar lightly on top of nail brush. Scrub nails, using sugar as exfoliant.