Especially in high frequency circuits there often seems to be the problem of ESR of capacitors. ESR apparently is a characteristic of non-ideal capacitors, and is essentially a resistance appearing in series with the capacitance of the component.
But after doing some Google searching I haven't been able to find much info on what actually causes ESR. I understand that caps have wires, which always have some resistance, but if wires are the cause of ESR, wouldn't all other wirings of the circuit usually cause much more resistance to be considered? Since caps are basically just plates with a dielectric in between, the only other source of resistance I can think of is the dielectric. But let's consider electrolytic capacitors for example: The dielectric is an electrolytic liquid, shouldn't the liquid conduct electricity quite well? Why would there be much resistance? Or if we consider ceramic caps: What causes resistance here?
I understand ESR much better in the context of inductors, which often have many loops of thin wire, which can be expected to introduce lots of resistance. But what really causes ESR in capacitors?