Serum vs Moisturizer vs Facial Oil. What's the difference?

Before elaborating on a Vitamin C serum’s in the skin care regimen, the serum's distinction from the facial moisturizer must be clarified.

Serums differ from moisturizers in that serums penetrate the layers of the skin, targeting deep into the skin tissue. This is why serums are usually of a thinner consistency than moisturizers, which only absorb into the surface layers of the skin. Think of it like a multi-vitamin for your skin. Serum is applied to cleansed skin before the moisturizer so that the serum’s concentrated rejuvenating ingredients can seep deep into the skin layers before the moisturizer can be applied on top to seal it in. This doesn't work the other way around, since the serum won't be able to seep into the skin if applied on top of a moisturizer.

Moisturizers on the other hand act as a protective barrier for your skin, keeping it hydrated and healthy. They reinforce the natural skin barrier to maintain the skin’s softness and suppleness. Moisturizers are thicker and creamier than serums. They're meant to hydrate the skin and prevent water loss. The anti-inflammatory properties help to quell irritated skin while reducing redness from conditions like rosacea.

Facial oils are super charged moisturizers that are great for providing intense hydration.
Because oils are lipophilic, they can penetrate deep into the skin, trapping water and other moisturizing goodness in, while keeping toxins and other bad stuff out. Some oils also help to fortify and strengthen our own natural skin barrier. This is especially important for big city dwellers who need extra protection against pollutants and smog, a known source of unwanted wrinkles. Facial oils absorb quickly and settle comfortably into the areas that need hydrating the most. This gives an immediate plumping effect while also shrinking pores to create the perfect canvas for your makeup — and the smoother your skin, the better your whole face will look.
Contrary to popular belief, facial oils can actually be great at treating pimples by reducing oil production.

Used together these three can form the foundation of a skin care regiment for those seeking to optimize their skin health and appearance.