This super-common smoothie ingredient has a rep for bringing on rogue breakouts

Once upon a breakout, after I had grown frustrated trying every single hormonal acne remedy out there, I decided to attempt the dreaded fight-acne-from-within strategy. Otherwise known as: cutting dairy, the inflammatory food that I’ve always loved so much. Le sigh.

I did diligently cut the stuff—or so I thought—until the breakouts kept on coming. I was confounded… until someone pointed out to me that something in my smoothie could likely be the acne-causing culprit: whey protein. After a quick Google, I realized that my friend was right, and then dermatologists affirmed that there is, in fact, a true link between whey protein and breakouts.

“Whey protein can cause or worsen acne,” says Cybele Fishman, MD, a New York-based dermatologist. I felt totally hoodwinked—although it was really my mistake, as whey protein is actually a dairy product. “Whey is a milk byproduct, and occurs when milk separates into cheese,” explains Purvisha Patel, MD, a board-certified dermatologist and founder of Visha Skincare.

To get into more of the scientifics behind it, Dr. Patel explains that acne is caused by a range of four different factors: follicular occlusion (blockage of your pores), microbe overgrowth in the follicle (bad bacteria in the skin), sebum production or adding an edible oil to the follicle, and inflammation (but of course). “Milk hormones increase the sebum production of the follicles, and whey protein increases insulin levels in the skin, which also increases sebum production,” she says. Dr. Fishman agrees, adding that whey is one of the major proteins in milk, and increases the production of a hormone called insulin-like growth factor 1, or IGF-1. “Insulin increases sebum, which can clog pores by stimulating too much testosterone production,” she explains.

But before you toss that smoothie on the spot, it’s not as if one whey protein-fueled smoothie is going to totally wreck your complexion (though it can still give you a breakout)—Dr. Patel says it really depends on your skin type. “Some people are extremely sensitive to the effects of whey protein and may not be able to tolerate any,” she says. “If you’re suffering from acne, stop whey protein altogether to help with your treatment and oil production.”

Dr. Fishman also recommends non-dairy protein sources, if you’re looking for something to replace your whey protein habit. The good news is you’ve got lots of options, from pea protein to hemp and brown rice. “Also, you’ll need plenty of water, sleep, multivitamins, and a probiotic for skin health as well,” says Dr. Patel. “There are plenty of other sources of protein out there. Diet and gut health impact your skin.” So if you’re breaking out and you think it could be linked to your protein powder, ditch the whey and see if things clear up for you.

To help with your complexion, you can also sip on these 9 smoothies for healthy, glowing skin. And here’s why you should be slathering on fermented beauty products, not just snacking on the kimchi.