Skin effect is a phenomenon in electromagnetism where an alternating electric current tends to become distributed within a conductor such that the current density is largest near the surface of the conductor and decreases exponentially with greater depths. The skin effect is where alternating current tends to avoid travel through the center of a solid conductor, limiting itself to conduction near the surface. This effectively limits the cross-sectional conductor area available to carry alternating electron flow, increasing the resistance of that conductor above what it would normally be for direct current. The skin effect becomes more pronounced as the frequency is increased.

Factors affecting skin effect include frequency, diameter, shape of the conductor, and type of material. Skin effect increases with the increase in frequency, diameter of the conductor, and permeability of the material. The shape of the conductor also affects skin effect, with it being more pronounced in solid conductors and less in stranded conductors because the surface area of the solid conductor is more.

Skin effect is a significant issue in high-frequency applications, such as radio frequency, where practically the whole of the currents flows on the surface of the conductor. Skin effect is an undesired phenomenon that leads to many disadvantages in the power system, such as an increase in effective resistance and a reduction of the cross-section area of the conductor.