Dark, dull, and yellow nails can be caused by various reasons such as smoking, nail polish and/or not enough nutrients. Hydrogen peroxide, white vinegar, denture tablet or Castor oil are a few of the ingredients you can use to have stain free nails.
To avoid discolorations start using a clear nail polish as your base coat. The proper nutrients in your body is essential Vitamin A helps in nail growth and Vitamin B2 promotes healthy nails. First, consult with your doctor before taking any type of vitamins. Definitely, if you can’t stop then try to smoke less.
Did you know…
Nail polish contains a colorless, toxic, water soluble gas called formaldehyde. Avoid buying nail polishes that contains formaldehyde this chemical is causing your nails to be dark. The chemical formula is CH2O and another name for formaldehyde is methanal. See link for more info Formaldehyde
Try which home remedy works best for you.
For home remedies view How to have stain free nails