I enjoy chatting with customers and often ask what they want me to blog about next. “Skin, how skin works, how skincare works” have been popular answers in the last couple of weeks. Because this is such a large and extensive topic, in order to do it justice I’m going to break this into segments and make it a series.
Skin has a lot of jobs. It is the front line barrier to foreign invaders (bacteria, viruses, fungi, toxins) and the environment, helps regulate our body temperature, and contains a complex system for allowing us to interact with our environment-permitting us to experience touch, pain, pressure, heat, cold, and irritation. Skin controls water loss and prevents nutrients from being washed from the skin.
On average a person has about twenty square feet of skin, making it the largest and heaviest of the body’s organs. Skin accounts for about 1/7 of a person’s body weight. Each square inch of skin contains approximately 20 blood vessels, more than 1000 nerve endings, and over 600 sweat glands. All this and it is only a few millimeters thick.
Skin is made of 3 layers: Epidermis, Dermis, Subcutaneous
The Epidermis is the outermost layer and the one we are the most acquainted with because it’s what we see every day. The epidermis is a waterproof barrier that gives skin its color, protects us from the external environment and creates new cells. The epidermis itself is about 0.3 mm thick, though on heavily used parts of the body (soles and palms) it can be up to 4 mm thick including calluses. The epidermis consists of 4 or 5 distinct layers, each with a different job.
The Stratum corneum is the top layer of the epidermis and consists of 20-30 layers of cells. This layer consists of dead keratinocytes. This tough horny layer makes our skin tougher and able to form thick calluses. It also seals the skin off from the outside environment; however, there are connective structions called dermal papillae that connect the dermis and epidermis allowing for oxygen, nutrients and waste to pass between the layers so it is not an impermeable layer.
Calluses are formed in response to pressure or rubbing. This causes the epidermis to grow faster and results in a hardened layer of skin on the surface. Only the cells directly beneath the pressure respond. This is why guitar players form calluses where their fingers are in contact with the strings, and a callus forms on the back of heels when wearing shoes that rub.
The layer Stratum lucidum is directly beneath the Stratum corneum in thick skin (soles & palms) only. This is a thin transparent layer consisting of two to three layers of cells.
Stratum granulosum is three to five layers of cells thick and contains lipid rich granules.
The Stratum spinosum is eight to ten layer of cells thick. The cells in this layer of epidermis are irregular in shape and look a little like spines.
Stratum basale is the deepest layer of the epidermis and is constantly producing new skin cells. This layer contains the skin pigment cells, melanocytes and also helps protect the skin from sun damage.
As the cells are constantly produced in the Stratum basale, they push the layers of cells above them. Each cell then passes through the different layers of epidermis and this takes about a month. So each cell you can see is only about 30 days old! You continually have opportunity to start treating your skin gently and make a difference in its life – and yours!
The middle layer of skin is the Dermis and it’s purpose is to protect the body from stress and strain. The dermis houses the hair follicles, lymphatic and blood vessels in addition to sweat glands, sebaceous glands, and receptors for pressure, pain and heat. This layer of skin makes sweat and oil, provides sensation recognition, and grows hair.
The dermis consists of two layers. The papillary region which has finger-like projections that push into the epidermis giving it a lumpy surface. These projections are responsible for fingertip patterns. The reticular region is the is the rest of the dermis and is made up of collagen, a tough elastic network of fibers that allow skin a stretch response. However, if skin is stretched a lot the dermis can tear and this is seen as light lines just below the surface. We know these as stretch marks. The dermis is approximately as thick as a sheet of paper, making it three times thicker than the epidermis.
The deepest layer of skin is called the Subcutaneous layer, hypodermis, or subcutis. It’s made up mostly of fat, connective tissue, and an elastic protein called elastin that help tissue return to their shape after stretching. The dermis also bulges into this layer and creates folds of tiny cavities that are filled with a tissue of fat and water. The fat behaves as a shock absorber and insulation. Many hormones and Vitamin D are produced inn the fat cells of the subcutis.
Throughout a person’s lifetime skin undergoes a great deal of change. It becomes thinner and more easily damaged, the insulating and shock absorbing capacities lessen, and the amount of collagen (and therefore the elasticity) decreases. Additionally, exposure to UV rays, hormonal changes, environmental, and genetic factors can add to premature aging.
There are measures we can take to keep our skin in the best condition possible. While we cannot permanently stave off aging there is a difference between aging and aging gracefully. I’m all about the aging gracefully and I think for today this is a pretty good foundation and place to stop. Next week we’ll take a look at the science of cleansers, and acne – Good stuff! Thanks for hanging out with me. 🙂