Kim Kardashian has admitted to three questionable skincare habits.

Whether it’s using mascara way longer than recommended or going months without washing foundation brushes, we’re all guilty of some pretty terrible beauty habits. After all, we’re only human — and so, it seems, is Kim Kardashian.

During a Master Class with her makeup artist Mario Dedivanovic (you know, the one who claimed responsibility for her “no makeup” Vogue Spain shoot) yesterday, the noted contouring enthusiast confessed to a couple of eyebrow-raising skincare behaviours. And if you’ve ever collapsed into bed without even swiping a makeup wipe over your face, you’re about to feel very vindicated.

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Yep, that’s skin sin number one: Kim Kardashian sometimes sleeps in her makeup. “Sometimes I’m just so tired and I don’t wash my face,” she admitted. Hey, we’ve all been there — although we reckon the 34-year-old should check out the ultimate lazy girl cleanser, micellar water.

However, Kardashian takes it one step further by, erm, re-using that trademark smokey eye the very next day, which is pretty hardcore. Her trick is to sleep “gently” on a black satin pillowcase.

“I’m sleeping on a flight and heading straight to an event when I land, I stop in the bathroom right after and touch up my foundation, but the rest is done… You just have to try to sleep as gently as possible, keep your eye makeup and then redo your foundation,” the TV star explained.

Yes, Kim Kardashian sleeps in her makeup. Then wakes up, and continues on her merry way the next day.

You probably don't need us to tell you sleeping in your makeup is a bad idea. If you need a reminder of why it's not wise, take it from Dermalogica's Education Manager of the Dermal Insititue, Emma Hobson.

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“Removing your makeup is such an important step in your daily skin care regimen to prevent skin sensitisation, as well as the challenges of increased skin congestion and possible eye irritations and infections," Hobson tells The Glow.

“Our skin needs to repair itself at night and allow several process to occur, including our oil production dropping and our skin temperature and pH fluctuating. The skin is also hotter and more acidic during nighttime.” (Post continues after gallery.)

Kardashian's second eyebrow-raising habit is using sun beds — apparently, though, this is not purely for tanning purposes.

"I have psoriasis so it's important for me to go to tanning beds every once in awhile," Kardashian, who is currently pregnant with her second child, says. She was diagnosed with the skin condition during an episode of Keeping Up With the Kardashians in 2011, after discovering a red spot. Her mother Kris Jenner also has it.

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Dr Michael Freeman, a dermatologist with The Skin Centre, says ultraviolet light is beneficial in the treatment of psoriasis but it's UVB light that needs to be used.

This is an important distinction to understand. There are three categories of UV light — A, B and C — and A and B can be useful in the treatment of skin diseases.

Generally, commercial sun beds use UVA light — and, as you might already know, exposure to it can increase your risk of skin cancer. This is why solarium use is being phased out across Australia.

"Yes, ultraviolet light is helpful for psoriasis, but the sun beds in tanning parlours are not helpful and can be dangerous and should not be recommended," Dr Freeman explains. "It's not clear whether [Kardashian] was talking about a tanning bed with UVA or UVB."

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If UV light treatment is appropriate for your psoriasis, Dr Freeman says a medical device that emits UVB light will be used — these are usually controlled and supervised by dermatologists, although it's also possible to have light boxes designed for home use. These devices still have a tanning effect.

Skincare habits aside, Dedivanovic's Masterclass also produced a makeup tip we've never encountered before. Apparently, you shouldn't forget to put foundation on... your ears. The more you know.

Do you ever sleep in your makeup? What about re-using it the next day?