The present invention relates to a cosmetic microemulsion comprising a non-ionic surfactant type emulsifying agent, a co-emulsifying agent and a solvent selected from the group consisting of hexadecane and isomers thereof and dodecane and isomers thereof, said cosmetic microemulsions having particle diameter smaller than 100 nm. Preferably, this cosmetic microemulsion is used in the form of a pre-shampoo and has particles with a diameter on the order of 40 nm.