Nail polish that has completely dried on the fingernails contains water-soluble components that attain the skin during extensive but transient contact. This was proven by water extraction of thin layers of nail polish that had been painted onto glass plates and allowed to dry for 3 days. Comparing the isolated fractions and compounds with known nail polish ingredients revealed that the water-soluble substances are para- and ortho-toluenesulfonamide, dibutyl phthalate and 3 constituents of toluenesulfonamide-formaldehyde resin (TS-F-R), which is the basic material of almost all nail polishes sold worldwide. 12 female patients with proven nail polish allergy were patch tested with 21 nail polish components, including those isolated. Only 2 fractions were positive. These contained a monomer and a dimer created during condensation of TS-F-R. Their structures were elucidated. The 3rd compound, a trimer, remained negative, except in 1 case.