History of the perm
It's thought that the first person to produce a practical thermal perming method was Marcel Grateau back in 1872. German hairdresser Karl Nessler took the process further with a curling hair method that reportedly used cow urine and water. Also involved in the process were heavy brass rollers and caustic soda applied straight on to the hair.
By 1930, the process of permanent waves was well established, with many middle-class women in the UK having their hair 'set' every few months. In 1938, the cold wave - essentially the precursor to the modern wave we are familiar with - was invented by Arnold F Willatt in 1938. In an innovative development, no machines or heat were used, although a 'reduction lotion' broke down the polypeptide bonds in the hair.
In the 1970s, acid perms were invented. These ammonia-free perms, sometimes called buffered waves, use glyceryl monothioglycolate instead of ammonia. The trend reached fever pitch in 1973 when then-style icon Barbra Streisand rocked a bubble perm in The Way We Were. In the next decade, countless stars followed suit with iconic looks, from Glenn Close's waves in Fatal Attraction and Olivia Newton-John's Grease makeover to Whitney Houston's power perm. Later, crispy curls were supplanted by a more shaggy, natural look - think Meg Ryan (above) in When Harry Met Sally.