THE SKIN & MELANIN
The skin is the bodies largest organ. It makes up about 16% of the total body weight.
The skin can be divided into 3 layers. The epidermis is the outermost layer, after which comes the dermis (the middle layer) and then, the subdermis.
The subdermis is made up of mainly fat cells, while the epidermis is composed primarily of nerve cells, blood vessels, and connective tissue (more on this later). The epidermis, which is divided into several layers, consists in a large part of Keratin (from the Greek word Keratos, or horn) forming cells. Keratin is what makes the skin tough. Keratin filled cells are formed at the bottom of the epidermis and work their way upward until the mature to form the outermost part of the epidermis (the skin we see and feel from the outside). In this way the top layer of the skin is always shedding and being renewed.
The epidermis also has a couple of other cell types that don't migrate to the top but instead, sort of float within the epidermis. The best known of these cells are the melanocytes, which produce Melanin. Melanin is a brown colored protein that helps determine the color of our skin. The difference between the fairest skinned and the darkest people is only a few grams of Melanin. The Melanin that the melanocytes make finds its way into the keratinocytes ( the cells containing the keratin) as they make their way up to the surface.
The melanocytes produce more melanin when we are exposed to the sun. The result of this is a "tan". The melanin's job is to help protect us from the damaging UVR. It's important to note however, that a tan is only partially protective. A "good tan" has an SPF of only about 4! A smart way to look at a tan is that the Melanin is the debris left over after the war between your skin and the sun - in other words - there is no such thing as a "healthy Tan" because to get that tan you needed to expose yourself to dangerous amounts of radiation. People who are born with very dark skin are naturally protected more that light skinned individuals but even the darkest people can get skin cancer and most certainly will show the signs of sun related aging (deep lines, sagging skin ..).
Also living in the epidermis are cells that are part of our immune system: Langerhans cells. Langerhans cells are there to help ward off invaders such as bacteria. They are also probably involved in recognizing and eliminating early skin cancers. A few minutes of unprotected UVR exposure will damage the Langerhans cells in ways that will last for weeks. In this way the sun delivers a double hit: first it causes damage that can lead to skin cancer then it cripples one of our body's normal cancer defense systems.
Below the epidermis is the dermis. The dermis is home to, among other things, collagen. Collagen is the most abundant protein in the body accounting for 30% of your dry body weight. There are 5 types of collagen each with its own characteristics and location: collagen is found in teeth, bone, skin, muscle, cartilage, and many other tissues. In the skin, the collagen provides strength and texture. In the dermis the collagen is formed into a bundle. It looks like a rope, made up of many twined strands. In the young, non sun-damaged skin, the individual strands of the "rope" are separate from each other. As one accumulates more and more sun damage the strands lose their orderly arrangement and, like an old rope, become frayed and tangled. Collagen damaged in this way is no longer strong and supple and this results in the sagging limp skin that we associate with aging. 90%of the changes in our skin that we commonly associate with aging are actually due to sun exposure and could be avoided with proper attention.
