Smoking is the biggest culprit that limits oxygen supply. It constricts capillaries, inhibiting blood flow and skin can take on an unnatural yellow-green cast. There are specific types of jobs that contribute to impaired oxygen supply. Airline personnel, such as pilots and flight attendants, surgeons and other medical staff that wear surgical masks. Also office jobs where the windows may not be opened and the air is constantly recirculated.
Discussion exists regarding whether cosmetic ingredients actually penetrate the skin.
These dead flat brown old cells have no sensory ability. Sensory nerve endings, which allow us to feel sensations such as pain or heat, exist deeper in the dermis. Therefore, we can feel a product such as those containing alpha hydroxy acids or ascorbic acid. They will sting or tingle when the product has entered the dermis. The dermis is where cell regeneration occurs.