Miley exits the tanning booth. Photo: Splash News.

Prior to meeting the Queen of England on Monday, Miley Cyrus committed one of the biggest beauty sins:

She used a tanning booth.

The teen star allegedly made a pit stop to SunSeekers Tanning Centre in Blackpool, seemingly to get a little sun before attending the Royal Variety Show that evening.

The star showed up at the tanning salon in a leopard coat and jeans, and left in a hurry -- in fact, she didn't even bother to put her jeans back on, instead just wrapping up in her coat and scurrying outside to her car.

Celebrity dermatologist Dr. Howard Sobel is displeased at Cyrus' actions, noting "Indoor tanning can actually be more harmful than being out in the natural sun, especially for young people."

"The UV rays you can get from tanning beds are more powerful and can penetrate deeper into the skin," Sobel explains. "If she goes to the tanning salon regularly, she will likely start to see sun spots, less firm skin, or worse."

Miley, are you listening?