"I'm rubbish – I'm really not good at my beauty regimes," she told us at the launch of her new make-up launch for Eyeko. "I use whatever's available to me. Dove soap is good or I use a Swedish cleanser made of egg whites that you can buy for five bucks in the States.
"I wash my face and then use lots of moisturiser."
The reason behind her low-maintenance skincare regime appears to be good genes. "I've been quite lucky because I don't really get spots," she said. "At school and as a teenager I never had spots so I don't really know how to deal with them."
She does, however, take care in checking the ingredients before applying anything to her skin, because of a bad experience. "I once got a lot of product sent to me that I used and had a bad overreaction to – it was a fine example of when a goody bag turns into a baddy bag really quickly," she said.
The make-up collection, which consists of a liquid eyeliner and mascara, is exclusively stocked at Selfridges, something that Alexa finds "surreal".
"When I was a teenager, I used to come to Selfridges and it was very swanky and overwhelming and I'd think 'Wow, this is amazing'," she said. "I would never have imaged having my own area in the beauty hall! It's incredible.
"I came down the escalator and say my face and thought 'God, that's weird.'"
Explaining her decision to bring out the eye duo, Alexa said, "Often I do translatlantic overnight flights from New York and when I land I have to do my eyes – I feel weird without it.
"Also I have really tiny eyelashes so I don't put anything on, my eyes disappear. It looks like someone stole the charcoal from the snowman's face!"
Widely considered one of the biggest fashion icons in the world – her style credentials include a Mulberry bag named in her honour, three British Fashion Awards for best style icon as well as several modelling campaigns – Alexa is recognised wherever she goes, something which can get a bit overwhelming.
"The attention sometimes gets a bit intense," she said. "When I'm walking down the street in New York just doing my own thing I kind of get surprised when people come up to me and ask for a photo – I get confused for a moment!"