Exam questions about nail products ask what an ingredient does and what risk it carries. These are the main ones the FDA and OSHA describe.
Formaldehyde in hardeners
Formaldehyde hardens nails by bonding with keratin, but the FDA warns that frequent use may make nails brittle and more likely to break or peel, and may cause skin irritation and allergic reactions. Anyone allergic to it should look on the label for any of its names: formaldehyde, formalin, methylene glycol or tosylamide/formaldehyde resin. OSHA links formaldehyde to cancer.
Phthalates in polish
Phthalates are used in nail polish, mostly at concentrations under 10%, as plasticizers that reduce cracking by making the polish less brittle. Dibutyl phthalate (DBP) is the one OSHA names.
Toluene
Toluene is a solvent in polish and glue. OSHA lists dizziness, dry skin and harm to an unborn child among its effects.
"3-free"
Toluene, formaldehyde and DBP are sometimes called the "toxic trio". Products labeled "3-free" claim to be made without all three.
Removers
Acetone removes polish; it is highly flammable and can cause headaches, dizziness and dry, cracked skin. Artificial nail removers are mainly acetonitrile.
Safety data sheets
OSHA requires safety data sheets for products with hazardous ingredients. Keep them for every product you use, and know where to find each one; clients may ask whether the salon has them.