Treatment of an abscess often requires that it be surgically drained because the wall of the abscess prevents neutrophils from entering the pus and attacking the pathogens.
Because of this abscess, your antibodies cannot enter it in order to fight it and rid your body of the disease. This is why it has to be drained as soon as possible so as to prevent further complications. If this wall is impenetrable, it means that nothing can go through it to treat it.
