Why do we blush?

I don't know.

When we are embarrassed, ashamed or shy, we blush.

Blushing is governed by our sympathetic nervous system.

Its functioning is not under our control.

What?

I cannot control my own sympathetic nervous system?

Absolutely.

Now, when we are ashamed or shy, it causes us immediate stress.

When something causes immediate stress, our sympathetic nervous system considers it as a threat.

To defend the threat, this system orders our adrenal glands to release a hormone called adrenaline.

Adrenaline speeds up our breathing rate.

It expands the blood vessels so that more blood and oxygen can be reached to our body parts.

Thus preparing our body for fight or flight.

Now, as the blood vessels on our face are very close to our skin surface.

They make our face appear red, that is, we blush.