British singer Zayn Malik. Picture: Bang Showbiz

Zayn Malik has revealed he is bald because he had "destroyed" his hair from constantly bleaching it and dying it various colours, but assured fans he's already growing it back.

The 24-year-old heartthrob shocked his fans when a picture of him completely bald appeared on his girlfriend Gigi Hadid's Instagram profile earlier this week and has now revealed the reason for losing his locks.

Speaking to Scott Mills on BBC Radio 1 on Friday, he explains: "I just shaved my head because I'd bleached it too many times and it was a bit destroyed.

"The bleach effects your hair doesn't it so you've got to shave it off."

However, the former One Direction star has assured his fans that he is growing it back.

He said: "It grows back straight away anyways, so I've got hair now anyway, it only took two days!"

The singer has experimented with his look ever since quitting the boyband in 2015 and previously rocked pink, green, grey and blonde hair.

A post shared by Zayn Malik (@zayn) on

Zayn - who has just dropped new song 'Dusk Till Dawn' with Sia - previously opened up about the restrictions he faced when in the 'History' group and how he and his bandmates - Harry Styles, Louis Tomlinson, Liam Payne and Niall Horan - weren't allowed to make changes to their appearances. 

However, in 2014 he "rebelled" and grew facial hair. 

He said: previously: "Eventually when I got older, I rebelled against it, and decided to keep it [the beard] anyway.

"That was just because I looked older than the rest of them. That's one of the things that is now quite cool. I get to keep my beard. I also wanted to dye my hair when I was in the band, but I wasn't allowed to."