Hypochondriacs, read no further. 

Burning mouth syndrome is a strange disorder with no known cause or cure, that can strike at any time. Its symptoms include an inexplicable burning feeling in the mouth, as well as a crawling sensation and occasional bitter or metallic taste. It’s been likened to the uncomfortable feeling you get when you bite into something that’s too hot. 

The syndrome isn’t deadly—it’s at worst painful and extremely annoying—but it is mysterious. It occurs when nerve fibers in the mouth begin functioning abnormally, sending pain signals to the brain without external stimulus. It’s like your mouth constantly thinks you’re drinking an incredibly hot cup of coffee and is desperately trying to tell you to cut it out.

Scientists still don’t know what causes burning mouth syndrome, though they can pinpoint risk factors. According to the American Academy of Oral Medicine (AAOM), it affects about 2 percent of the population and is seven times more likely to strike women more than men—especially postmenopausal women. It’s also been known to coincide with stressful life events like job loss or the death of a loved one, though no causal relationship has been discovered. 

Perhaps the strangest thing about the disorder is that, for many sufferers, it stops when they fall asleep. Patients have reported a brief respite from symptoms when they wake up in the morning, though the pain starts to come back over the course of the day. Scientists don’t yet understand why the burning sensation is alleviated by sleep.

Fortunately, long-term cases of the disorder are extremely rare: For most people, it only lasts a few weeks. While there is no cure, low doses of medications used to treat anxiety, depression, and other neurologic disorders can help ease the unpleasant symptoms, according to the AAOM. 

[h/t: io9]