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."