What effect causes the apparent resistance of a conductor to increase significantly at higher signal frequencies?

Answer

The current flows predominantly near the outer surface ("skin").

The skin effect, prominent at higher frequencies, causes current to flow primarily near the conductor's surface, effectively reducing the cross-sectional area available for current flow and increasing apparent resistance.

What effect causes the apparent resistance of a conductor to increase significantly at higher signal frequencies?
resistanceSignalLosscircuitAttenuation