The Structure of our skin
November 1, 2008
Skin is something we all have, but how much do we know about it? This post explains how the skin is structured and how it absorbs substances like body care products applied to it.
Key skin facts:
- Skin is the body’s largest organ
- Our skin can absorb 0-100% of what is put on it (1)
- An average adults skin measures two square metres
- It is less than 2mm thick in most places
- The epidermis completely renews itself in 45-75 days
- Skin accounts for about 16 of a persons body weight
- Skin acts as an insulator and protects the organs
Skin is made up of 3 parts:
Epidermis (outer layer/horny layer)
The epidermis is a flat layer of skin (made from about 15 individual layers of skin) that is constantly flaking off. When you exfoliate, you are removing dead skin cells from this layer.
The epidermis is made from cells called keratinocytes – they have this name because they produce a protein called keratin. Keratin is important because it gives the skin it’s strength to resist physical wear and tear and also makes the skin waterproof.
The other layers of skin below the epidermis are constantly producing new cells. At the beginning of their life, these cells are square and sit at the base of the epidermis layer. Over time, their internal structure starts to break down and they become flatter. As they become flatter, they ‘rise’ to the surface and turn into the outer layer of skin.
This layer gets its name from the Greek word for skin. The dermis is mostly made up of collagen and elastin. Collagen is a protein naturally found in connective tissue and elastin is a protein made from thin stretchy fibres. The dermis has two parts: the upper area is made from lots of blood vessels and nerve endings and the lower area is a thick mesh of fibres.
This layer holds the hair follicles and the sweat glands. The hair follicles are shafts that run the whole depth of the dermis and up through the epidermis where they appear on the surface of the skin. On the side of each hair follicle is a very small gland that produces sebum. The pores of the skin start deep in the dermis layer and are spiral shaped sweat ducts that travel up to the surface of the skin.
This layer of skin attached to the deepest level, called the subcutaneous layer.
The third and bottom layer of the skin is called the subcutaneous layer and is made up of connective tissues and fats. This layer has a number of roles:
- To protect the internal structure of the body
- To hold everything in
- To insulate the body
Absorption of substances
The skin is a barrier to external elements, but because it’s porous, it cannot repel everything. There are several factors that can affect the skin’s absorption of substances:
Molecule size of the substance
Substances with larger molecules cannot penetrate the skin as easily as ingredients or products with small molecules…think of it like trying to push a slice of bread through a sieve. The smaller the molecule size, the further into the skin, the ingredient can penetrate. For example, many suncreams now contain nanoparticles. Nanoparticles are microscopic particles that are used because their size means they can penetrate the skin easily…making the rate of absorption much quicker.
Condition of the skin
If the skin is damaged (sore, bleeding, broken skin etc) then a product/ingredient can be more easily absorbed. When skin is healthy the cells lay flat and overlap. If skin is damaged/irritated, then this structure can become uneven, making it easier for substances to penetrate as they can enter through the gaps. An example of this would be a sheet of plastic. You pour water onto the sheet when it is in tact and it runs off, but pour the water on it when it is cracked and it can start to move into cracks in the plastic.
Length of exposure
A ‘leave on’ product like a face cream will have longer to penetrate the skin compared to a product like shower gel which gets washed away almost as quickly as its been applied.
Temperature and humidity
Studies have shown that higher temperatures and humidity can have an affect on skin absorption. The reason for this is that when the body is hot, blood vessels in the skin expand. This increased blood flow to the skins surface releases heat from the body. When you are cold, the blood vessels in your skin contract which cuts off the amount of blood flowing to the skin – this body heat is conserved in the internal organs. The increased blood flow to the skin means that substances that have been absorbed are easier to carry into the body and into the bloodstream.
- (1) Response from Sense about Science
- A Consumer Dictionary of cosmetic ingredients (6th edition). Ruth Winter, M.S.
- Net Doctor: Skin Structure
- Sense About Science: Harmful chemicals in make-up and household products
- Oxford Journals: Factors Affecting the Extent of Dermal Absorption of Solvent Vapours: A Human Volunteer Study
- Image: Encarta – Structure of the Skin