Q: Does bleeding from the gum or teeth invalidate prayer? And could we swallow some of it?
A: It does not invalidate prayer and if the blood reaches the cavity of the mouth, it is not permissible to be swallowed because it is one of the Najassat that should not be swallowed. Moreover, if he/she takes the blood out of his mouth by a tissue it does invalidate the prayer even his lips become not pure, as long as his mouth is bleeding.