For people with very light skin, the skin gets most of its colour from the bluish-white connective tissue in the dermis and from the haemoglobin associated blood cells circulating in the capillaries of the dermis. The colour associated with the circulating haemoglobin become more obvious, especially in the face, when arterioles dilate and become tumefied with blood as a result of prolonged physical exercise or stimulation of the sympathetic nervous system (usually embarrassment or anger).[41] Up to 50% of UVA can penetrate deeply into the dermis in persons with light skin pigmentation with little protective melanin pigment.[2]