[thedoc (OP)]

"GAMEL,JOHN"  asked the Naked Scientists:
   
Under great emotional stress, the human face tends to one extreme or the other: "pale as a ghost" or "red as fire." Obviously in one instance all the blood drains from the face, while in the other the tissues become suffused with blood.
 
I think fear causes pallor while anger causes dilation of the blood vessels, but I'm not sure if this is always true. And in either case, what is the physiological basis?
 
John Gamel, MD

What do you think?

[cheryl j]

Redness in the face can be the result of dilation of blood vessels in the skin from an overactive sympathetic nervous response. It happens when we're angry and when we blush from embarrassment. Emotional environmental stimuli send messages to the hypothalamus in the brain, which stimulates sympathetic nerves - part of the fight or flight response. Fear should trigger the same response. I'm not sure why sometimes it results in pallor instead, although paleness could be related to a sudden drop in blood pressure, like that which also causes people to faint when they are emotionally traumatized or see something gorey. This kind of drop in blood pressure is caused by stimulation of the vagus nerve.