Please switch off my face when you leave the room.

Even though it happens rarely, I can sometimes turn on a classic red blush. I never see them coming; the only common denominator seems to be that they make their appearance in front of men. And the fact that the reaction embarrasses me tends to exacerbate the situation. A pasty bitch like me has no hope of disguising it.

I was going through my old copies of The New Scientist when I noticed this article. It seems that the psychological reasons for blushing are still a mystery, although the cause - increased adrenalin levels - is known.

In a species with a reputation for cunningly manipulating others to maximise personal gain, blushing is pretty difficult to explain. Why would humans evolve a response that puts us at a social disadvantage by forcing us to reveal that we have cheated or lied?

It is a question that Charles Darwin struggled with. He pointed out that while all people of all races blush, animals - other primates included - do not. When it came to explaining the evolution of "the most peculiar and the most human of all the expressions", he was at a loss. That has not stopped others from trying.

One suggestion is that blushing started out as a simple appeasement ritual: a way to show dominant members of the group that we submit to their authority. 

The article continues, but it gets technical and a tad boring. Besides, i'm not buying into a lot of it. For example, my own blushing isn't triggered by cheating or lying; it's more of a shyness thing. Sexual situations seem to contribute now and then. And it can fire up if I tell someone a secret about myself, which is rarely.

My only guess as to the source of this habit is that it's somehow triggered by adrenaline-fueled sexual arousal, even when I don't consciously realize it. Because who doesn't get pink when fucking?