Originally Posted by
MaxAstro
This is not actually how 2e works, but is a common confusion because it did work that way in 1e.
In 2e, there is positive healing, and positive damage, which are separate things. A creature with the negative healing trait takes damage from positive damage, and is unaffected by positive healing, but does not take damage from it. This is why, for example, the Heal spell specifies that it does positive damage to undead.
In no case does positive damage heal a creature, and in no case does positive healing damage a creature. Same with negative energy.