For many people, it sounds strange, but the skin is the biggest organ of our body, which is exposed to the strongest environmental impact every day. During life, the skin accumulates various lesions and therefore is a visual “aid” for aging of the human body.

Skin aging at this stage of evolutionary development is an inevitable process, but someone manages to prolong the youth of the skin for many years, and someone quickly fades. There are many factors involved in this injustice. This is the impact of genetic material and environmental factors.  However, knowledge of some biological laws, as well as the most damaging factors of the skin will help to maintain the health of the skin and prevent the development of a large number of diseases.

1. What is the skin made of?

The skin of the human body consists of 4 layers:

The 1st layer is called corneum. In fact, it is the upper layer of the epidermis, which consists of corneocytes. They are tightly attached to each other, and the intercellular space between them is filled with lipids. The main function of the corneum layer is to protect the inner layers.

The 2nd layer of the epidermis itself. Its main task is the production of the corneum layer. In the lower layer of the epidermis there is a basal membrane, with basal keratinocytes located on it (responsible for corneocytes formation and skin renewal), melanocytes (responsible for pigment formation) and Langerhans cells (immune cells) .

The third layer is the dermis. The main function of the dermis is nutrition of the epidermis. It contains lymphatic and blood vessels, while the epidermis has no vessels in its structure. In addition, collagen fibers in the dermis are responsible for the elasticity and stiffness of the dermis, as well as elastin fibers that allow the skin to stretch and return to its previous condition. The space between the fibers is filled with gel-like substances (mainly hyaluronic acid) that hold water. Between the fibers there are dermis cells — fibroblasts, which are small factories to produce various compounds.

The 4th layer is represented by adipose tissue. It consists of lobules separated by a fibrous tissue. There are fatty cells inside the lobules.

2. How does UV radiation affect the state of individual skin structures?

As you know, one of the most aggressive environmental factors that damage the skin and cause premature aging is ultraviolet radiation. The wavelength of UV radiation can be divided into three types:

• UV-A (315-400 nm)
• UV-B (280-315 nm)
• UV-C (100-280 nm)

UV-C rays are absorbed by the ozone layer, while UV-A and UV-B rays penetrate into the environment. In this case, UV-A rays have the greatest penetrating ability and reach deep layers of the skin:

Fig. Effects of rays of different wavelengths of the UV spectrum on the skin (by Alexandra Amaro-Ortiz at al)

UV-A and UV-B radiation affects the genetic apparatus of skin cells, causing various mutations in them. The mechanism is that the DNA of the skin cells easily absorbs the energy emitted by sunlight. At the same time, the smaller the wavelength, the easier the DNA molecule to absorb energy, respectively, the stronger the impact in the series UV-A, UV-B, UV-C. This leads to rupture the chains of the molecule and their subsequent reunion, but in unusual places. Thus, there are damages in the genetic material and there are deviations in the “behavior” of the cell. Such exposure can be called direct DNA damage.

In addition, UV radiation can indirectly damage cell macromolecules, causing the formation of free radicals and active oxygen forms — highly reactive compounds that damage the DNA molecule and capable of inducing mutagenesis. Such exposure is called indirect DNA damage.

In both cases, DNA damage and free radicals lead to the depletion of basal keratinocytes, slowing skin renewal, as well as damage to fibroblasts, thereby reducing the amount of produced proteins responsible for the “quality” of the skin. Damages accumulate and skin resources are depleted, which leads to premature aging.

References:

1. Amaro-Ortiz, A., Yan, B., & D’Orazio, J. A. (2014). Ultraviolet radiation, aging and the skin: prevention of damage by topical cAMP manipulation. Molecules (Basel, Switzerland), 19(5), 6202–6219. doi:10.3390/molecules19056202
2. Panich U, Sittithumcharee G, Rathviboon N, Jirawatnotai S. Ultraviolet Radiation-Induced Skin Aging: The Role of DNA Damage and Oxidative Stress in Epidermal Stem Cell Damage Mediated Skin Aging. Stem Cells Int. 2016;2016:7370642. doi:10.1155/2016/7370642
3. Марголина А.А., Эрнандес Е.И.- Новая косметология – Практическое пособие Том 1
4. https://www.who.int/uv/uv_and_health/ru/