This we know, atoms make up the physical world. It stands to reason ghosts are made from particles smaller than atoms since they are capable of passing through solid objects such as doors and walls. There are particles smaller than atoms called Neutrinos (ghost particles). These particles scientists have known, can pass through solid objects.
Neutrinos are like photons, they don't carry an electrical charge and if they did atoms would repel them. If a ghost can be detected by electrical meters and can disrupt electrical charges, then it makes sense that ghosts carry an electrical charge themselves.
It's been theorized ghosts might be made up of plasma. The fourth state of matter, (solid, liquid, gas and plasma). Plasma is comprised of highly energized ions and electrons, which might explain the glow surrounding ghosts. Could ghosts, or more likely ghost lights, or luminous plasma orbs be a misunderstood form of plasma?
For plasma to go through walls, it would need to be of a lower density. Dark matter, or "collision-less plasma" as scientists like to call it, is an invisible substance that has the ability to pass through itself or something similar.
Depending on the frequency of the plasma a ghost would appear translucent or clear making the apparition light or dark?
Theories abound. To this date, no one knows what ghosts are made from.