Ik that this is just a fantasy story that makes no sense if you think about it too deeply but...
If his cold is caused by a bacteria, wouldn't that mean that the curse does not kill microorganisms and only multicellular ones...
If his cold is caused by a virus, isn't that objective evidence that virus are not alive...
And to add on it, a flower wilt because its cells are drained of water which causes them to shrink and the overall integrity of the plant to be very weak. Does that mean that the curse induces rapid water evaporation in plants?