One reason for our ears to turn red is that at times our sympathetic nervous system kicks in on its own and causes our bodies to release adrenalin and noradrenalin. Noradrenalin is the chemical responsible for relaxing the smooth muscle in the walls of the blood vessels. When the smooth muscle in the blood vessels relaxes the diameter of the vessel increases and the volume of blood passing through the blood vessel also increases. This is referred to as vasodilatation. When this happens the skin feels warm and may have a pink or red colour. This usually happens when we feel nervous or stressed and is part of the "fight or flight" mechanism, even though the only "threat" may be social. However, in some people the sympathetic nervous sytem is overactive. This can be caused by inherited genes. We have no conscious control over the sympathetic nervous system so it kicks in without our decision to be "embarassed."

I can't really say why . .

But I have an unfailing how ( well for me anyway )

I good cup of strong chocolate ( or sometimes a square or two ) gets them going fearsomely.

MSG ( sadly still in use at many a behind-the-times Chinese restaurant ) hits the spot too.

I suspect therefore a chemical messenger of some kind  is at work . . .

My Mother would say someone is talking about you!

You do not state the times of day, nor whether you habitually blush vigorously at embarrassing thoughts. If you light up mainly in the cold season then perhaps simple cold damage to your skin or mild frostbite is the cause. You needn't be exposed to severe cold to experience this; even in South Africa "winter oor" (Afrikaans for "winter ears") are a common nuisance.

In susceptible people exposure to temperatures below about 10 °C may bring it on. Sandals or bare feet invite winter toes as well. Cryophilic bacteria may then infect cold skin, aggravating peeling and itching. These bacteria do poorly at normal body temperature, so keeping the affected area warm and applying antiseptic compresses at a temperature of about 45 °C will generally clear things up.

Arterioles in some people's extremities go into spasm for various reasons, especially in reaction to cold. This starves the skin of blood, most familiarly in the hands. This is known as Raynaud's syndrome. When the blood vessels relax and the affected areas warm up the skin commonly flushes red and may become painful.

Jon Richfield, Somerset West, South Africa