Scientists Discover Whether Fear Alone Is Enough to Literally Curdle Blood

Blood can thicken in anxiety-inducing situations that involve actual physical danger. But is the same possible when the fear is 100 percent in your head? Glen Hadiardjia/Getty Images

People are gluttons for punishment. Just ask Chicago Cubs baseball fans, whose passion for the team seems to only get stronger with each passing decade of ineptitude. The same goes for scary-movie goers, who hit the theatres to be so frightened, thrilled, disgusted or horrified that they might just have trouble getting to sleep at night.

Whether it's the creepy theme music from "The Exorcist," the human skin suit that some deranged redneck prances around with in "House of 1000 Corpses" or the woman in the bathtub in the Overlook Hotel's room 237, the best parts of scary movies are the ones that make us feel physically scared. A recent study out of the Netherlands shows that there just may be some science behind the idea of "bloodcurdling fear."

The team studied blood levels in 24 volunteers under the age of 30, who were asked to watch an educational and a scary movie on varying days. For frights, the team had their subjects take in "Insidious," the story of a family plagued by supernatural spirits and featuring a healthy amount of things going bump in the night. The researchers found that the scary movie caused some viewers' blood to actually start changing form by producing a blood-clotting protein called Factor VII (itself a potential title for a horror movie).

"We already know that people who are stressed out, or freaked out, like by bungee jumping, show temporary increases in FVIII," says Frits Rosendaal, an epidemiology professor at Leiden University Medical Centre who helped run the study. "But, such fear or stress is usually accompanied by physical exertion."

Blood clotting might sound gross, but it's actually a good thing. It can prevent a person from bleeding to death when their blood vessels are cut or damaged, whether it's in an accident or during a surgical procedure. FVIII levels rose by about 11 percent on average among the study participants when their blood was tested after watching the horror movie.

That's not enough to suggest that the action on the screen can actually cause a person's blood to fully clot, according to Rosendaal. But it could be enough to help aid the process in which blood turns from liquid to gel. "The system was more alert," Rosendaal says of the FVIII levels.

The team intends to continue researching the impact of acute fear on coagulation to see whether fear can be used to help people whose blood doesn't easily clot. Are we heading towards a future where hemophiliacs get prescribed hours of Wes Craven movies?

In the meantime, horror movie lovers can tell their squeamish friends with a semi-straight face that watching someone get hacked to pieces on the big screen could actually help save their lives. 

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