A composition for chemically modifying the internal region of a hair shaft, wherein the composition comprises: an ethylenic monomer having a molecular weight of 500 g/mole or less； a cation and an anion； wherein the cation is selected from the group consisting of inorganic cations having a charge density of 0.05 charge/picometre or more； a cosmetically acceptable carrier； wherein the composition has a pH of from 4.0 to 6.9.
