Why do we blush with embarassment?

Two certain facts: animals don't blush, and people don't blush in private. Why then do we blush with embarrassment? And to add to that, the harder you try to stop yourself from blushing, the more your face gets red!

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Blushing is a complex reaction that psychologists have variety of explanations. Blushing is an involuntary reaction that is dictated by our mind, but a part of our mind over which we have no control. Whenever you blush, tiny blood vessels supplying your face and its surrounding area suddenly dilates or widen, allowing more blood to flow through than the usual.
Some people blush in an instinctive reaction when they commit what they believe is unreal, or when they have done nothing wrong. For instance, many people get embarrassed by praise. Maybe they are shy, or they prefer to be swallowed up by a crowd instead of being singled out from it.
Dr. Murray Blimes of Berkeley, California said that " The striking thing about blushing is its implicit mixed signal. A blush is a funny mixture of wanting to hide and at the same time wanting to attract someone".
For adolescents, a tendency to excessive blushing usually vanishes with age. This is such a consoling fact for teens.

Reference : Reader's Digest Why In The World