Q: Why does nail polish stain your nails yellow?
A: As you might've guessed, it's the coloured pigments in the nail polish! Generally, the pattern is that the staining is darker at the tip and fades towards the cuticle. It's a bigger problem when the dyes are dissolved rather than suspended in the polish (e.g. with stearalkonium hectorite).
If you've worn polish only for a week (snort), the colour should fade in two weeks after you remove your polish. If you're more impatient, you can try scraping the top of your nail off, since the colour sinks in from the top, but be careful as this will weaken your nail! There are also a bunch of whitening products on the market, but for most of us die-hard polish addicts, the only real solution once your nail is stained is to wait for it to grow out (or cover it up!).
To prevent staining, you should use a base coat, and try to avoid polishes containing the dyes that tend to penetrate your nail the worst. Have you noticed that your nails always end up yellow-orange, and never blue or green? The reason is that certain dyes sink into your nails more. Common culprits are D&C Red Nos 6, 7 and 34, and FD&C Yellow No 5 Lake.
Have you got any tips for unyellowing your nails? Share them in the comments! :)
P D Samman, Nail disorders caused by external influences. J Soc Cosmet Chem 1977, 28, 351.
R Baran and J André, Side effects of nail cosmetics. J Cosmet Dermatol 2005, 4, 204.