Franklin: I often suggest to clients that they scrub their nails with good old-fashioned soap and water and tell them not to dig under their nails with sharp implements as they usually end up just shoving dirt farther under their nails. If that doesn’t do the job, I suggest scrubbing with a manicuring brush (or old toothbrush) and a whitening toothpaste. But for really ground-in dirt and oil (for those mechanic’s hands), I recommended soaking them in warm water mixed with a small portion of Blue Gross Cuticle and Stain Remover. It will remove most dirt and stains from the nails and cuticles, but you must be careful not to overexpose the skin to this product. Don’t soak for more than 10 minutes and only in a diluted solution.
Other remedies to try include soaking in Polident denture cleaner, which will whiten and brighten nails as well as remove many stains, or soaking in a 50/50 mix of white vinegar and water for 10 minutes a few times a week.