This is the terrible truth behind Marilyn Monroe's iconic hairdo

If there's one Hollywood figure who will always arouse fascination, it's Marilyn Monroe. From her doll-like physique to her incredible career and her tragic death, she is and will always remain a film and glamour icon. But what's the star's most recognisable trait? Her angelic blonde hair and pin-up curls that lay perfectly around her face. This is one of the characteristics that made Marilyn so famous—however, it's not exactly natural.

From dull, dirty blonde to platinum blonde

In her youth, Marilyn Monroe was beautiful, but plain. Her hair was a little bland and did not really fit what people were looking for. Before a photo shoot, the young model therefore agreed to change her hair colour and go for that almost white blonde we all know.

But in the '40s, bleaching techniques were even more harmful to the hair than they are today. Achieving this legendary blonde required high doses of sulphuric acid and hydrogen peroxide, which burns your hair and scalp.

They also added a hair-colouring agent to this, which was made with hydrogen peroxide and many other ingredients that are now known to cause allergies and asthma. The whole process had to be repeated two to three times a week, to touch-up the roots and avoid the blonde turning yellow.

Drastic hair straightening

In addition to being naturally darker, Marilyn's hair was very curly. She was therefore advised to perm and straighten her hair to define her curls and give them that signature vampy look. To achieve this result, they had to use caustic soda, in order to completely destroy the nature of the hair. This ingredient is also used to unclog pipes. That should give you an idea of its long-term effects on hair.

Oil baths, masks on masks... Nothing could be done to repair the actress's hair, which had become porous, rough, dull and brittle. To give the impression of voluminous and healthy hair, Marilyn Monroe always went for big, curly hairstyles. In her last days, the star even had to wear a wig to hide the disastrous results of all this damage to her hair.

Take a look at the video above for another look at some of Marilyn's most iconic hair looks...