How many steps to a “skincare regime”? The more steps, the more products you will be using.
How many? Is the number determined by your skin’s needs or the needs of the company selling to you skincare products?
The many steps of skincare are more a tradition than a scientific opinion, but some steps are easy.
Clean first, makes sense. Remove whatever life deposited on your skin during the day driving in a city, or cooking or working in your garden and getting all of that pollen and spores stuck to your clothes (and skin). So, go ahead and cleanse your skin but without the harsh detergents that will remove all those lipids that make it a great barrier to the outside.
What the last step should be is also straightforward: sunscreen, which will prevent damage by UV, blue light, and all the ROS* produced by the interaction between light and your skin.The objective of sunscreen is mainly to reflect UV light, and some ingredients will absorb it and turn it into more benign energy, like heat. No need to absorb anything in the sunscreen so you can leave it for last.
What about the “middle”? Whatever you apply to the skin will be absorbed, so the order does not matter very much. If you take a shower before applying skincare products, then apply first the water-based serums, because the hydrated skin will absorb the water-soluble actives more easily. Then apply oil-soluble serums, like those containing essential fatty acids. If you are using a cream, that makes life easier: a cream is an emulsion of water and oil and all the actives will be nicely dissolved in the cream.
Whatever serum you choose, it must help deactivate Reactive Oxygen Species (ROS*) in the environment and those made by your own cells. These ROS* are big contributors to skin aging, DNA mutations, protein modification, and more.