If you frequent American beauty websites, you might be familiar with the term "Big 3" and its relevance to nail varnish. If you don't and you're wondering what all the fuss is about, well sure grab a cuppa, sit back and relax and we'll have an auld gab about them!
The Big 3 are formaldehyde, dibutyl phthalate (more commonly known as DBP), and toluene. Formaldehyde is used as a preservative and strengthener, and while it's more often found in treatments (and, eh, morgues!) than polishes, a resin form of formaldehyde which is a pretty common allergen may be used in nail varnish to help it harden and prevent chipping. DBP is a specialist plasticiser that makes nail varnish flexible. Toluene is a solvent makes nail varnish flow better, which in turn makes for easier application.
Now these three chemicals are considered by many to be dangerous and toxic, and there has been a big push from most nail varnish producers to reformulate their products in order to eliminate these ingredients. The good news for nail varnish fanz on this side of the Atlantic is that there is actually an EU-wide ban on the use of dibutyl phthalate in cosmetics, while the use of formaldehyde and toluene is strictly regulated and their presence must be declared on the labels of any nail products they're in.
Where you might need to be really aware of all this Big 3 business is if you purchase nail varnish and nail care products over the Internet. As I mentioned earlier, most companies are making the transition to 3 Free formulations - 3 Free colours from Orly have a grey rather than black cap, for example - but in fact formaldehyde, DBP and toulene aren't deemed harmful in cosmetics by the FDA as long as the product's being used as intended.
This means that products containing the Big 3 may still be available for purchase through online stores, or for swap on international sites like MakeUpAlley. (You're unlikely to have that problem with our very own homegrown Swap Siopa, hem hem).
If you want to check whether that must-have nail varnish is 3 Free before you click purchase, take a look at All Lacquered Up - Michelle has posted a great list of what brands are using which formulations which is the most comprehensive I've been able to dig up for you.