Hi, hello, a skin layer with dead cells on top of it here - epidermis!
So most importantly, I’m a barrier between you & outside world, keeping those dust-dirt-bacteria-viruses-irritants-etc OUT and water IN.
And let’s be honest, products you use at home stay on/in me, *epidermis*, and don’t really penetrate much deeper unless it’s a drug formulated to do just that or I’m seriously damaged/removed.
WHAT I LOOK LIKE
So imagine a brick wall. Oh actually, that’s it. Bricks are specific skin cells, mortar is lipids such as ceramides, fatty acids & cholesterol holding those cells together. In order to pass this wall, not only a molecule should be super small, but also have some lipophilic properties to slip through the lipids.
NOW ATTENTION: I do not have any blood vessels in me. Those ones are in the deeper layers (dermis & hypodermis). This will come handy when busting “skincare in my bloodstream” claims ;) I do have some nerve endings, though. If my barrier function is impaired, & you walk into the salty sea or spill lemon juice on the skin - it may hit the unprotected nerve ending, resulting in stinging/burning/itching.
I am pretty thin - have you ever had a paper cut? Remember, I don't have blood vessels, so if blood is showing - you just cut right to the dermis layer. That’s thin to a human eye, but keep in mind, from a molecule perspective, it’s hella road to travel!
HOW SKIN TURNS OVER:
My lowest layer [basal layer] has live cells [basal cells], which continuously divide into new cells, pushing previously created ones upward. When they’re nearing the surface, they go through keratinization process -> cells are filled with keratin protein, flatten, lose their nucleus and, there’s no easy way to put it, DIE.
Those dead skin cells form the topmost stratum corneum layer, where cells shed naturally & by the help of exfoliation. This process usually takes 28 - 40 days, & slows with age.
Mortar & brick structure is quite a defence provided by the lipids between the cells - that’s why over-washing & over-exfoliating the skin is not the greatest idea - long live the lipid barrier!
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