With Justin Bieber’s DUI arrest this morning came the addition of a new celebrity mug shot to add to the ever growing pool.

But as thousands gawk at Bieber’s awkwardly cheerful photo, many on social media have also been commenting about the quality of his skin – well, the poor quality of it, that is.  Bieber’s mug shots showcase more than one blemish, leading some to wonder if he’s been neglecting his skin cleansing regimen.

As recently as 2013, Bieber was a spokesperson for the acne treatment Proactiv, filming commercials to promote the product.   In one commercial, Bieber claimed that Proactiv helped to clear up some pimples on his chin, which had been caused by holding a microphone too close to his face.

When asked for a comment on Bieber’s pimply appearance, a representative for Proactiv declined, as the celebrity hasn’t been a spokesperson for the company since March 2013.

So what’s the deal? Is the singer not being proactive with his Proactiv?  One dermatologist said it’s possible that the product may not actually be working for him.

“Some of the Proactiv products do have effective acne treating ingredients,” Dr. Joshua Zeichner, director of cosmetics and clinical research in the dermatology department at Mount Sinai Hospital, told FoxNews.com. Zeichner has not treated Bieber. “That being said, not all acne responds to over-the-counter products.  After four to six weeks, if your skin isn’t improving with over-the-counter acne treatments, you should visit your dermatologist.  Because there are medications we can give by mouth.”

There are a number of other reasons why Bieber could be suffering a breakout – including all of the negative press he’s been receiving lately.

“There are many environmental factors that can lead to breakouts, and those include emotional stress,” Zeichner said.  “Some of the hormones that increase during stressful periods can actually stimulate our oil glands to go into overdrive.  And more oil means more food for the acne-causing bacteria on our skin.”

As for Bieber’s lifestyle choices, his newfound partying probably isn’t to blame.

“There’s been no association between alcohol use and the development of acne,” Zeichner said.  “But in terms of diet, diets rich in sugary foods have been associated with acne breakouts in predisposed people.  Then there’s an association with cow’s milk in some patients.  I’m not telling people not to drink milk, but it’s something to consider.”

So what is ultimately causing Bieber’s breakout? Other than being your typical teenager, the world may never know.