People are chewing on rock hard gum to firm their jawline and look more sculpted, but experts say the craze is not safe or effective, according to The New York Times. Teenage boys are crediting brands like Stronger Gum or Jawliner for giving them a chiseled, more masculine appearance, but experts doubt the before and after photos on social media are the real deal.

On their website Jawliner claims that the gum “strengthens, tones and defines your jawline” by training the masseter muscle along with 40 additional facial muscles if you chew the product 10 minutes daily. The gum is pricey, selling for $26 for 60 pieces. The company says that 60% of their customers are 18 to 25 years of age.

One cosmetic dentist says that to reap the alleged benefits of the gum, you’d have to chew for eight hours a day for years. Some of her clients have presented with jaw pain or damaged fillings from chomping on facial-fitness gums.

“The risks definitely outweigh the benefits,” said Dr. Daniela Eversgerd.

The American Dental Association said that excessive chewing can lead to inflammation and jaw pain. The association added that some of the products contain caffeine and vitamin B5, which may have a laxative effect. The ADA recommends that people with temporomandibular disorders avoid chewing the gum.

 According to The Cut, before and after photos of young men with decidedly stronger jaw features allegedly from using the gum may have been photoshopped or altered in some way.

Dr. Paul Jarrod Frank, a cosmetic dermatologist, says that chewing facial fitness gum will not change the underlying structure of the jawline, and that the wider, more square-shaped jaws that appear on TikTok and other social media sites like Instagram may be the result of a “dramatic difference in lighting, giving the impression of greater definition.”

Tomas Palomaki, the founder of Stronger Gum, says that chewing should be limited to 30 minutes daily, says the Times, and also encouraged anyone with TMJ disorders to check with their doctor before trying the facial fitness products.