Emily Weiss has to shampoo her hair four times before it is clean.

The 36-year-old businesswoman - who is CEO of the cosmetics company Glossier - admitted that her favourite shampoo "is a weird" mask that requires several rounds usage to work.

She said: "[My go-to] is actually a shampoo called Christophe Robin Lemon Cleansing Mask. I’ve gone through about 12 jars, it’s my favourite. It’s a weird shampoo – It doesn’t sud so you have to apply and wash it like four times for hair to be really clean – but despite that, I love it."

Emily - whose company was launched back in 2014 and the brand is now estimated to be worth $1.2bilion - explained that despite the "rigour" of the routine, it can be beneficial to scalp health.

She told Vogue: "Afterwards you don’t need any conditioner and your scalp health is great. It’s rigorous, but it works."

When it comes to taking out for herself, Emily - who is currently expecting her first child with fiancé and businessman Will Gaybrick - revealed that she unwinds by taking a bath with a "giant bag" of Epsom salts to relax.

She said: "The number one thing that always helps me is taking a bath – so maybe I’m English if I take a bath every night. It’s a transition from daytime to night-time. I get home from work, take a bath, and there’s a real before and after. Straight away my whole body is completely relaxed and I’m in a totally different headspace. I always dump a giant bag of Epsom salts in the bath – they’re cheap and you need a lot of them, not just a scoop. I have so much Epsom salt real estate in my house – that’s the base."