Natural = the same exact thing as 3- and 4-free
Unless someone figures out a way to whip up a Nobel Prize-worthy liquid pigment derived from say, rose petals, that then magically adheres to nails, an all natural polish is simply not happening.

“Natural’ is a term that is overused and is ambiguous when it comes to nail polish,” says Creme. “Even if you take out the ingredients that have been shown to be harmful, the formulation is still chemically based, so it can’t be truly natural—and there’s no shame in having a chemical formulation that’s safe.”

Hey, if there are some natural ingredients in your polish that are doing your nails some extra good (i.e. vitamin E or hydrating natural oils), great, but otherwise, be wary of a company claiming their polish is natural and read the label closely to see what backs up their claim. 

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Acetone = highly flammable solvent with an eye-watering smell
Nail polish remover has been traditionally formulated using acetone or ethyl acetate solvent. “These ingredients are flammable, harsh and drying to skin, and generate a lot of fumes, which can irritate the eyes, lungs and skin,” says Hammer.

Hammer suggests looking for less toxic removers that are acetone-free and contain less irritating solvents, including propylene carbonate, ethyl lactate (which comes from corn), methyl soyate (from soybean oil), and d-limonene (from oranges). All of these materials are capable of dissolving polish, although you’ll have to put a few more rubs into in than with acetone-based versions.

Whichever kind you choose to use to wipe away polish, minimize exposure by soaking a cotton pad thoroughly then pressing it onto nails for a few seconds before rubbing. “This technique helps dissolve polish quickly so that you don’t have to use more than you need,” says Hipp. “And always sit in a well-ventilated room or even go outside where there’s plenty of fresh air.”

Benzophenones = UV blocker that prevents color fading
So, you know how after a few days into a beach vacay your freshly painted, shiny and bright nails suddenly turn drab, dull and well, kind of yellow? That’s because just like your beloved highlights are prone to the havoc of oxidization, so is your polish.

That’s exactly why so many companies use benzophenones in an attempt to shield ultraviolet light from degrading polish for as long as possible (it’s also in inks as well as in perfumes and even soaps—and of course the mother of all sun protectors, sunscreens, where it acts as simply a UV light defender). The problem is that there are studies showing that it exhibits estrogen-like effects and is a carcinogen when used in large quantities.