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This is usually not because these are "bad" energy forms; but because there is an injury in the energy body and when these specific energy forms touch that injury, pain is experienced.
When an injury is healed, the energy form can enter freely and flow in, through and out, energizing the energy body in the process (which shows that it wasn't a "bad" energy form after all), and the shield is no longer necessary and can be removed.
Shields block often vital energy forms and cause problems with the systems of energy nutrition, leading to a form of energy malnutrition for the owner of the shield.
Shields can be dissolved easily by application of attention and intention.
Shields can also be created deliberately and under conscious control for purposes of energy magic.