New research shows the fluid used in popular “bee stung” lip injections can result in lesions caused by antibiotic resistant bacteria. People looking to plump their lips or smooth their wrinkles with temporary ‘filler’ treatments may want to consider a serious but relatively unknown complication of the procedure: drug-resistant bacterial infections. A new study published in the journal Pathogens and Disease shows that side effects of the common plumping injections aren’t allergic reactions, but rather disfiguring lumps and lesions caused by the injection of bacteria under the skin. Researchers in Denmark say that the fluid being injected, hyaluronic acid, is an excellent incubator for bacteria and can lead to very hard-to-treat infections. Learn What Dangerous Ingredients to Avoid in Cosmetics »

An Increasingly Popular Treatment Treatments based on hyaluronic acid—such as Restylane—are the second-most popular non-surgical cosmetic procedure in the U.S., according to the American Society for Aesthetic Plastic Surgery (ASAPS). While the rate of bacterial infection is estimated to effect around 1 in 1,000 patients, the growing popularity of the procedure puts more people at risk. “Most people are unlikely to have any problems undergoing a filler treatment to smooth their skin,” researcher Thomas Bjarnsholt, an associate professor at the University of Copenhagen’s Department of International Health, Immunology and Microbiology, said in a statement. “However, it’s a bit like driving a car: there’s nothing wrong with not wearing your seatbelt as long as you don’t hit anything. If you do have an accident, however, it’s almost impossible to walk away unharmed.” Read More: Facelifts Only Shave a Few Years Off of Your Appearance »

More Than a Simple Infection While safety precautions are always taken to prevent infection, there is a risk whenever the skin is broken, even by something as small as a needle. In the past, most experts believed the side effects of hyaluronic acid were caused by an allergic or autoimmune reaction, but the Copenhagen researchers examined tissue from patients and mouse models to determine that bacteria are the culprit. “What is more, we have demonstrated that the fillers themselves act as incubators for infection, and all it takes is as few as ten bacteria to create an ugly lesion and a tough film of bacterial material—known as biofilm—which is impossible to treat with antibiotics,” said Morten Alhede, a post-doctoral researcher at the University of Copenhagen. According to the American Society of Plastic Surgeons (ASPS), the average cost of hyaluronic acid in 2009 was $592 with added fees. But the procedure, and any medical attention needed due to complications, is not covered under most insurance plans. Neither the ASAPS nor ASPS list infection—bacterial or otherwise—as a possible complication of the treatments on their websites. Busted! Learn the 7 Myths of Dieting »