Did you know that the surface layers of skin, also called the stratum corneum, is anywhere between 9~11 layers? Cosmetic brands aren’t allowed to speak about penetration beyond these surface layers, so if you are seeing claims like ‘reproduces collagen’, an action that takes place in the dermis beyond the stratum corneum, note that this is actually against FTC regulations. Regardless, penetration of products and actives – even within the...