How real is the fear factor?

by | Heart Attacks and Strokes

Do scary movies actually elicit a bloodcurdling response?

We often hear people refer to scary things as ‘bloodcurdling’. That is, the feeling of extreme fear or danger eliciting changes to the flow of blood. This is based on the concept that the feeling of horror might make the blood curdle or clot, perhaps in some people, causing heart attacks or strokes.

Researchers have explored the effects of physical stress, including adrenalin and anxiety, on the body’s coagulation (clotting) system, finding that increased stress correlates with increased coagulation activity. Whether or not this response applies to fear that’s unrelated to physical situations is not well known. Researchers looked at the effect of fear brought about by scary movies on the clotting system.

Twenty-four healthy volunteers were shown a horror movie and a documentary. To measure coagulation, the researchers took participants’ blood samples before and after each viewing.

The markers investigated were blood coagulant factor VIII, D-dimer (a small protein fragment present inthe blood after a blood clot is degraded), thrombin-antithrombin complexes (used for the diagnosis of disturbances in blood coagulation) and prothrombin fragments.

Participants also completed a fear scale questionnaire after each viewing that estimated the level of fear generated after watching each movie.

The questionnaire showed that participants viewed the horror movie as frightening and the documentary as not scary.

Coagulant factor VIII was higher in most people after the horror movie than the documentary, with these levels increasing in 12 participants during the horror movie and only three in the documentary.

Furthermore, these levels fell in 18 people during the documentary but only in nine during the horror movie. No significant effect on levels of D-dimer, thrombin- antithrombin complexes or prothrombin factors were observed.


This study suggests that the acute fear many of us feel after watching a scary movie might have real effects on our blood flow. Increases in coagulant factor VIII can correspond to increase risk of developing thrombosis (a blood clot).

So for all of the horror movie fans out there, there might be more to the phrase ‘bloodcurdling’ than meets the eye.