All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
The blood which comes out from festers on your own body and you did not cause them to bleed, by pressing or peeling, is pardoned whether it is a small or large amount. Also, you are permitted to perform the prayers while wearing these blood-stained clothes. There are two conditions for this pardoning:
First: one should not be the reason behind this bleeding. For example, if one killed fleas and therefore his body or clothes were stained with a large amount of blood, this is not pardoned.
Second: there should be no negligence involved. People have their habit and custom in washing clothes. If one left his clothes unwashed, for a year for example, this is not pardoned.
Allaah Knows best.