What is meant by “natural repair processes”?

Skin essentially repairs itself at night, so that by day, it can perform its main function, which is protection.

At night, when it is safe from environmental stress – and, of course, from daylight - the cell can focus its energy on its regeneration and repair.
As it no longer needs to defend itself, the skin’s physiology alters, and one can observe an activation of the blood microcirculation, an improvement in cellular exchanges and improved cutaneous permeability.

All of these elements contribute to improve the cellular metabolism, hence better repair.