Dr Anjali Mahto, consultant dermatologist at Skin55 and author of The Skincare Bible: Your No-Nonsense Guide to Great Skin, tells us that milk has been used in skincare for thousands of years.

“Cleopatra was documented regularly bathing in donkey milk in an attempt to keep her skin supple and youthful and she may have been onto something,” she says.

“Milk contains lactic acid, a type of alpha hydroxy acid (AHA) which is commonly used in many chemical exfoliators. Lactic acid, however, is a larger molecule compared to many other AHAs and therefore takes longer to soak into the skin, making it a milder form of exfoliation than many commonly available products.”

Dr Mahto says that a regular soak in milk may offer mild exfoliation and work to remove dead skin cells over time, making skin feel softer and appear rejuvenated “without damaging the skin through vigorous scrubbing or using stronger exfoliants”.

However, she isn’t convinced that the results are worth the hassle – or the money.

“Adding a glass of milk or two to a bath will certainly feel luxurious, however the true skin benefits can be more easily achieved with a good skincare regime,” she says.

“Regularly filling an entire bathtub with high-quality milk such as organic goats’ milk would not be cost-effective, and the results achieved in comparison to using carefully selected products with clinically proven ingredients mean that a milk bath should not be relied on as part of an effective skincare regime.”

Carey isn’t the one celebrity to enjoy a milk bath. Last year, Holly Willoughby revealed that she often relies on milky baths to help her relax and “switch off” in the evenings.

Explaining that she picked up the tip from beauty expert Liz Earle, the This Morning presenter said that she mixed “old school dried milk powder, like your nan used to bring on holiday to put in your tea” with dried rose petals and lavender essential oils.

“Then you just take a scoop and put it in your bath to make a milk bath – it’s so soft!”

We asked a skincare expert whether Mariah Carey’s milk bath treatment actually works