Big 3 Free

The term Big 3 Free refers to 3 formerly common ingredients in nail polish, which are thought to be the most toxic ingredients found in polish. These ingredients are formaldehyde, Dibutyl Phthalate (DBP), and toluene. Most nail polish companies no longer use these ingredients, but the switch affected nail polish formulas. The typical Big 3 Free formula initially, was often described as thick-but-runny, making it harder to apply. Most companies that are Big 3 Free have overcome these initial hurdles in formulation. Big 3 Free polishes usually smell less strongly compared to older more chemically laden polishes - even the same brands. Currently, some nail polish brands are becoming Big 4 Free, which means free of the previous 3 ingredients, as well as formaldehyde resin. There are not conclusive rulings on the danger of these ingredients in nail polish.

Formaldehyde
Formaldehyde is not used in nail polish, but can be found in some nail treatments, such as nail hardeners (including top coats). Formaldehyde resin makes polish, "tough and resilient" and helps it stick to the nail. Formaldehyde is a carcinogen at certain levels.

Dibutyl Phthalate (DBP)
Dibutyl Phthalate is a plasticizer sometimes used to prevent chips and cracks. DBP is banned for use in cosmetics in the European Union. DBP is not banned in cosmetics in the United States, but it is suspected of causing child birth defects and being an endocrine disruptor.

Toluene
Toluene is a solvent that acts as a paint thinner, making polishes more easy to apply and work with. Toluene has been linked to cancer.

Links
Polishes Categorized by Ingredient (not exhaustive)