An Irish woman claims her gums were "severely burned" during a teeth whitening session gone wrong.
Áoife Wills is worried the damage is permanent and will need a gum graft after the treatment left the skin around her teeth blackened, reports the Daily Mail.
Wills, from Monaghan in the Republic of Ireland, shared photos of her gums to her Facebook page, claiming that the unnamed salon didn't use protective gel.
"Just a warning to people!! On Saturday I went to a beauty salon in Monaghan to get my teeth whitened, I put my trust in these people to do their job correctly!" she wrote.
"However I have now been left with my gums severely burnt and in serious pain! I had to go to the dentist today to get them checked and get an X-ray, thankfully my teeth haven't been damaged I am very lucky."
She said the dentist didn't yet know how her gums would heal, as there should have been protective gel put on them before the procedure.
"Simply their fault!! Seriously anyone looking to get teeth whitened please go to a dentist and get it done correctly!" she said.
Teeth whitening uses bleach powder or gel to lighten the enamel on teeth.
According to the UK's NHS, it's illegal to carry out teeth whitening by untrained or unqualified staff in beauty salons and it should always be done by a qualified dentist.
Badly-fitted mouthguards can cause the bleaching gel to leak out onto gums and into the mouth, causing severe blistering. The bleaching agents and chemicals also damage soft tissue, which can discolour the skin.
Wills' post was shared over 2,000 times, as social media users reacted in horror and sympathy.
One wrote, "That is a b***** disgrace, I would be taking it further no joke. And you should be getting your money back also."
"That's a f***** joke. Name and shame them. Can't believe a place would leave anyone like that. I hope it heals well for you," commented another.
Wills said the damage would most likely be permanent, saying it was a "lesson learnt" but the pain hadn't eased up.
"People really need to be careful who they go to! I wouldn't want to see anyone else go through this pain," she said.
"Only ever let a dentist near your teeth."