Define and discuss the difference between permeability (penetration) and absorption. Permeability represents the amount of a topically applied substance that exists between the top and the bottom layer of the epidermis. There is no absorption into the blood and cannot affect the body systems. Skin absorption occurs when the applied chemical reaches the dermal layer and absorbs into the blood stream. Briefly discussed how skin care ingredient penetration works. Small particle size products are permeable and can be uptaken by skin cells. After a period of time they will be secreted out of the skin cells and enter the blood. Large particles will move between the skin cells and enter the circulation. Non absorbed particles may be temporarily absorbed by some glands and absorbed over time.