The perm has shown its staying power ever since. ... Early, haphazard techniques gave way to "cold waves" involving chemicals but no heating and 1970s "acid perms" which were gentler on the hair.

The perm really took off in the Seventies, with the arrival of gentler “acid perms”. 15. Julia Roberts wowed fans with a perm in the 1990 film Pretty Woman Credit: Alamy.

There are different perm treatments (acid and alkaline) for different hair textures. “Acid perms usually have a pH rating between 4.5 and 7.0 and require heat. These are [comparatively] less ...

The perm has shown its staying power ever since. Everyone from pop stars Kylie Minogue and Madonna to England footballer Kevin Keegan has worn the look, with the "permanent wave" adapting to suit ...