Toothache medication turns woman's blood blue

blue blood
Doctors measured her oxygen level at only 67 percent of what it should be. Photo credit: New England Journal of Medicine

Marrying a prince isn't the only way to turn your blood blue.

A woman in the US managed to turn her actual blood literally blue after applying too much numbing pain reliever on her gums.

"I'm weak and I'm blue," she told doctors at Rhode Island's Miriam Hospital when she checked in, NBC News reports. 

The bizarre case is detailed in the latest issue of the New England Journal of Medicine.

The 25-year-old had a toothache, so applied topical benzocaine. But she put on too much, and the benzocaine started stripping electrons from the iron in her blood - stopping it from bonding properly with oxygen.

Without enough oxygen, her blood turned blue. 

Doctors measured her oxygen level at only 67 percent what it should be - low enough to cause tissue damage.

Dr Otis Warren told NBC once they took some blood from the woman, he knew right away it was methemoglobinemia - which he'd seen once before.

"The skin colour looked exactly the same. You see it once, and it stays in your mind."

They injected her with a treatment ironically called methylene blue, and she was feeling better within minutes.

She was sent home fully recovered the next day after a second dose, and told to see a dentist.