Why are parents dying their kid's hair? The 'unicorn hair' Instagram trend explained.

Hair colour isn’t just for adults anymore.

With the school holidays upon us in most states, “unicorn hair” has been popping up on kids all over social media.

And if you’re feeling a little confused by this latest hair trend, mummy blogger Mel Watts, aka The Modern Mumma, is here to explain.

Mel shared a photo of her five-year-old daughter, Ivie, with purple streaks through her blonde hair on Instagram on Monday.

“Today we coloured her hair. She’s about as happy as a rabbit in a carrot field. She also feels like she looks like a mermaid, hence the fish lips,” she wrote.

And others are also keen to try out the trend.

“What did you use… 25 and I want mermaid hair,” commented one follower.

Mel says Ivie had been begging her to colour her hair for weeks in the lead up.

“Ivie asked me if she could have purple hair like the mermaids a few weeks back,” she told Mamamia.

“Knowing the school holidays were upon us, I decided we could do it then. By the time she goes back to school, it will have faded.”

Today we coloured her hair. She’s about as happy as a rabbit in a carrot field. She also feels like she looks like a mermaid, hence the fish lips – ????????‍♀️ “babe mermaids don’t have fish lips under the sea, that’s actual fish” …. ????????‍♀️ #nofilter her eyes are just this ridiculous in certain lights. #unicornhair no nasties ????????‍♀️????????‍♀️ – not sponsored.

A post shared by m e l w a t t s (@melwatts) on Apr 16, 2018 at 3:34am PDT

The mum-of-four says she kept things natural by using dye from a company called Lime Crime, which produces “vegan and cruelty-free makeup”.

“I bought a tint called Moonchild… I bought it purely because it’s designed to fade out,” she added.

The tint that Mel used on Ivie is semi-permanent, and she says it left her daughter’s hair “really soft and smelling amazing”.

“Even since doing it last night, it’s already faded. I haven’t done it before, but I do believe it lasts a few weeks,” she said.

And the colour was an immediate hit with her daughter.

“She thinks she is a mermaid. She loves it,” said Mel.

Even though the product claims to be “ultra conditioning” and “damage-free”, Mel can understand if some parents aren’t keen on the idea of colouring their kids’ hair.

“Everyone has their own parenting style. I know my parents would never have let me do it, and once they see her, I’m sure they’ll question it,” she said.

“Each to their own. We don’t have to parent the same, we don’t have to like things others do, but as long as we are kind, that’s all that matters.”

LISTEN: ‘Your hair should never be more interesting than you are.’ Post continues below.

For parents who are keen to get onboard the trend though, Mel recommends they test a small section of their child’s hair first.

“Don’t leave it on for too long if you’re unsure. Its a really light colour from what I see with Ivie,” she said.

“I can’t guarantee how it will look on other children. But unicorn hair is fun, so is mermaid hair, and I figure they’re only this little once.”