Sunlight has taken some hits in recent decades. Skin cancer, age spots, wrinkles -- it seems there's little we can't blame on UV radiation.
And here's another: Excessive exposure to UV rays can potentially cause fingernail damage, including color change and brittleness. To prevent this, cosmetics manufacturers have introduced the SPF topcoat, a clear finishing layer that protects nails from the sun.
The thing is, nail polish -- any nail polish -- protects nails from the sun. A single coat provides a nice barrier to the sun's harmful rays. Three coats provides a fortress. A topcoat adds a moat. If you have a manicure, additional sun protection factors are superfluous.
On your nails, that is. Hands, feet and cuticles, presumably not shaded by three or four coats of enamel, need all the sunscreen they can get.
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