A constantly runny nose may be a sign of cerebrospinal fluid rhinorrhea, or CSF rhinorrhea.

Sometimes a runny nose is just a runny nose, but sometimes it's far more serious.

That's what Arizona resident Joe Nagy discovered when he went to see a doctor after suffering from a runny nose for over a year.

"I got to the point where I had tissues all the time in my pocket," Nagy told Fox 10 News.

Nagy's doctor told him his runny nose was actually brain fluid leaking out through his nasal cavity. [10 Things You Didn't Know About the Brain]

"I was scared to death, if you want to know the truth," Nagy said.

Nagy's medical condition is known as cerebrospinal fluid rhinorrhea, or CSF rhinorrhea. And it's not as uncommon as you might expect, though still a rare medical condition.

In 2012, after enduring a runny nose for months, Aundrea Aragon discovered she, too, had CSF rhinorrhea.

"I knew it could not be allergies," the Arizona resident told FoxNews.com. "The fluid would come out like a puddle."

CSF rhinorrhea is caused by a small tear or hole in the membrane surrounding the brain. It can result from a severe head injury, complications from surgery or high pressure in the skull (intracranial pressure).

Because the brain produces roughly 17 ounces (500 milliliters) of cerebrospinal fluid each day, a runny nose caused by CSF rhinorrhea can be a seemingly endless problem.

And because a runny nose is such an ordinary complaint, most people ignore CSF rhinorrhea at first.

"This is one of the more common conditions to be missed for a long time … because so many people have runny noses," Dr. Peter Nakaji, neurosurgeon at Barrow Neurological Institute in Phoenix, told Fox 10 News.

In some cases, the leaking can stop on its own, but there's a real danger in ignoring the condition: Left untreated, the cerebrospinal fluid can become infected with life-threatening meningitis.

In Nagy's case, he had to be treated for his meningitis before doctors could operate on his CSF rhinorrhea.

The surgery usually involves repairing the hole in the leaking membrane; the operation is performed through the nasal cavity in most cases and does not require cutting into the brain or skull.

After dealing with his runny nose for about 18 months, Nagy wasn't sure his operation would be successful.

"I was waiting for the dribble [because] I was so used to it every day," he told Fox 10 News. "I got my hankie … nothing. It's never come back."

Follow Marc Lallanilla on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on LiveScience.com.