The fact that Purpura and Ecchymosis are two terms mostly used to describe certain discolorations under the skin is the reason why people usually get confused about their possible differences. Purpura refers to the appearance of red or purple discolorations on the skin, caused by sub dermal bleeding. These reddish purple discolorations don't blanch even when pressure is applied on them.
The word purpura is from Latin language which means purple or red. Purpura can occur due to a lot of causes. Vascular disorders, platelet disorders, coagulation disorders, meningitis, vitamin c deficiency, are some of the major causes of purpura. On the other hand, ecchymosis is the appearance of a reddish or bluish discoloration on the skin, usually caused by the exudation of blood from damaged blood vessels.
Most times, ecchymosis is usually referred to as a bruise. This is because ecchymosis can occur when blood vessels under the skin have been damaged by a blow. Another cause of ecchymosis is blood coagulation disorders. In the case of purpura, the patches of blood are smaller in purpura compared to ecchymosis.