3 things are needed for Oxidation to occur: Heat, Oxygen and UV radiation, all happen every day on a boat left in the elements, eliminate one of them and you can slow down the process.
Oxidation is the actual Gel coat breakdown, its a chalky white powdery substance that results from a chemical reaction within the polyester Gel coat itself. The powder embeds itself into the pores in the Gel coat, that is what gives your boat the milky appearance.
Think of Oxidation as " rust " on Gel coat, it is the same as rust on metal, you can't repair it correctly without removing the rust.
Once Gel gets that bad the only way to restore it is to wetsand and compound the pores open to flush out the broken down Gel coat.
Dark colored gelcoat absorbs much more UV and heat from the sun than lighter colored gelcoat. Consequently, it breaks down rapidly into short-chain, low molecular weight “chalk” . This can happen in such a way that “pores” or micro crevices are eaten down into gel-coat. This situation is analogous to the way in which rust forms on metal. It starts on the surface and then eats down into the metal. Abrasives only remove the surface chalking and cannot reach down into the deep pores filled with chalk. In fact, abrasives can remove good gelcoat and scratch up the surface greatly increasing surface area exposed to new oxidation.
Oxidation is a direct result of not having a good wax coat or sealant on your Gel coat. This wax layer diffuses (refracts) both UV and infrared radiation from the sun. Without the wax/sealant coating, the radiation is absorbed by the pigment in the gel coat causing it to over heat, and trigger the chemical reaction that will dry out, dull and oxidize the surface.