Why does nail polish turn your nails yellow?

What's in nail polish?
Nail polish ingredients include a film-forming substance, a solvent and pigments.
Nail polish ingredients include a film-forming substance, a solvent and pigments.
© iStockphoto.com/pederk

Nail polish, also called nail enamel or nail lacquer, has evolved throughout the centuries thanks to scientific research. Most nail polishes on the market today are non-toxic, yet contain chemicals to help with application, drying, glossiness and long-lasting adhesion to the nail.

Ingredients you'll find in nail polish today are:

  • A film-forming agent, most often nitrocellulose, which is also used in auto painting
  • A solvent, which is the volatile part of your nail polish
  • Diluents, such as ethyl acetate, that lower and stabilize the viscosity of the solvent while keeping the nitrocellulose from separating out
  • Resins and plasticizers, like dibutyl phthalate and castor oil, to ensure the lacquer finish "gives" instead of chips when your nail bends
  • Pigments, and sometimes reflective particles, to give the polish its color
  • Additional chemicals to adjust the viscosity of the polish, which affects ease of application and drying time
  • Ultraviolet stabilizers that prevent the polish from changing color in UV light

In recent years, manufacturers have started to introduce water-based nail polishes. The polish still needs a filming agent, a solvent and a pigment, but the manufacturers aim to avoid petrochemical solvents. The target market for the new formula is consumers who are sensitive to the ingredients in other polishes, or those looking for environmentally friendly cosmetics.

In the United States, any colors added to nail polish must be certified by the Food and Drug Administration. Your polish color is some combination of pigments from organic dyes and other sources, such as iron and chromium oxides (for creating red and yellow) and ultramarine (for creating blue). Creamy polishes use titanium dioxide to add opacity, and pearlized polishes include either natural pearl (guanine crystals), or the cheaper alternative bismuth oxychloride.