UNDERSTANDING SKIN & DERMATOLOGY BASICS
The skin is the body’s largest organ. It creates a barrier between the external environment and the internal organs. The skin has several important functions vital to human life. Its thickness varies depending on where it is located on the body. For example, the skin on the face is thin compared to the skin on the back.
The skin is an ever-changing organ that contains many specialized cells and structures. The skin functions as a protective barrier that interfaces with a sometimes-hostile environment. It is also very involved in maintaining the proper temperature for the body to function well. It gathers sensory information from the environment, and plays an active role in the immune system protecting us from disease. Understanding how the skin can function in these many ways starts with understanding the structure of the 3 layers of skin – the epidermis, dermis, and subcutaneous tissue.
The epidermis is the outer layer of skin. The thickness of the epidermis varies in different types of skin. It is the thinnest on the eyelids at .05 mm and the thickest on the palms and soles at 1.5 mm.
THE EPIDERMIS CONTAINS 5 LAYERS. FROM BOTTOM TO TOP THE LAYERS ARE NAMED:
• stratum basale
• stratum spinosum
• stratum granulosum
• stratum licidum
• stratum corneum
The bottom layer, the stratum basale, has cells that are shaped like columns. In this layer the cells divide and push already formed cells into higher layers. As the cells move into the higher layers, they flatten and eventually die.
The top layer of the epidermis, the stratum corneum, is made of dead, flat skin cells that shed about every 2 weeks.
Specialized Epidermal Cells
There are three types of specialized cells in the epidermis.
• The melanocyte produces pigment (melanin)
• The Langerhans’ cell is the frontline defense of the immune system in the skin
• The Merkel’s cell’s function is not clearly known
The dermis also varies in thickness depending on the location of the skin. It is .3 mm on the eyelid and 3.0 mm on the back. The dermis is composed of three types of tissue that are present throughout – not in layers. The types of tissue are:
• elastic tissue
• reticular fibers
Layers of the Dermis
The two layers of the dermis are the papillary and reticular layers.
• The upper, papillary layer, contains a thin arrangement of collagen fibers.
• The lower, reticular layer, is thicker and made of thick collagen fibers that are arranged parallel to the surface of the skin.
Specialized Dermal Cells
The dermis contains many specialized cells and structures.
• The hair follicles are situated here with the erector pili muscle that attaches to each follicle.
• Sebaceous (oil) glands and apocrine (scent) glands are associated with the follicle.
• This layer also contains eccrine (sweat) glands, but they are not associated with hair follicles.
• Blood vessels and nerves course through this layer. The nerves transmit sensations of pain, itch, and temperature.
• There are also specialized nerve cells called Meissner’s and Vater-Pacini corpuscles that transmit the sensations of touch and pressure.
The subcutaneous tissue is a layer of fat and connective tissue that houses larger blood vessels and nerves. This layer is important is the regulation of temperature of the skin itself and the body. The size of this layer varies throughout the body and from person to person.
The skin is a complicated structure with many functions. If any of the structures in the skin are not working properly, a rash or abnormal sensation is the result. The whole specialty of dermatology is devoted to understanding the skin, what can go wrong, and what to do if something does go wrong.
THE SKIN HAS MANY FUNCTIONS, INCLUDING:
• protecting the body from heat, sunlight, injury and infection
• helping to regulate body temperature
o Blood flow to the skin’s surface allows the heat to escape to the air and helps to maintain a constant body temperature.
o Sweating allows the body to regulate its temperature. Sweating does not occur until the core body temperature is greater than 37°C.
• helping to control fluid loss
o The skin prevents the body from losing water and electrolytes. Yet, as a balance, water continually evaporates from the skin’s surface.
• getting rid of waste substances through the sweat glands
o Nerve receptors in the skin monitor the environment by sensing cold, heat, pain and pressure. These nerve receptors are more concentrated in our fingertips.
• storing water, fat and Vitamin D
There are five basic skin types, including:
1. Normal skin
This type of skin has a fine, even and smooth surface due to its ideal balance between oil and moisture content and is therefore neither greasy nor dry. People who have normal skin have small, barely-visible pores. Thus, their skin usually appears clear and does not frequently develop spots and blemishes. This type of skin needs minimal and gentle treatment, but does still require maintenance.
2. Dry skin
Dry skin has a parched appearance and tends to flake easily. It is prone to wrinkles and lines due to its inability to retain moisture, as well as an inadequate production of sebum by sebaceous glands. Dry skin often has problems in cold weather, which dries it out even further. Constant protection in the form of a moisturizer by day and a moisture-rich cream by night is essential. It is important not to over-exfoliate even in cases of extreme flaking, as this only dries out the skin further; gentle exfoliants using sugar, rice bran or mild acids are the most suitable, although they should not be used more frequently than once per week to avoid causing irritation and dryness.
3. Oily skin
As its name implies, this type of skin surface is slightly to moderately greasy, which is caused by the over secretion of sebum. The excess oil on the surface of the skin causes dirt and dust from the environment to adhere to it. Oily skin is usually prone to blackheads, whiteheads, spots and pimples. It needs to be cleansed thoroughly every day, especially in hot or humid weather. Moisturizing with an oil-free, water-based and non-comedogenic moisturizer is required in addition. Exfoliation is also necessary, but over-exfoliation can cause irritation and increase in oil production; exfoliants that contain fruit acids are particularly helpful, and fine-grained exfoliants may help to clear blocked pores, discouraging breakouts and improving the skin’s appearance.
4. Combination skin
This is the most common type of skin. As the name suggests, it is a combination of both oily and dry or normal skin, where certain areas of the face are oily and the others dry. The oily parts are usually found on a central panel, called the T–Zone, consisting of the forehead, nose and chin. The dry areas usually consist of the cheeks and the areas around the eyes and mouth. In such cases, each part of the face should be treated according to its skin type. There are also skin care products made especially for those who have combination skin; these contain ingredients that cater to both skin types.
5. Sensitive skin
Sensitive skin has a tendency to react to many potential triggers with irritation, redness, stinging or burning, flaking, lumpiness and rashes. The most common causes of irritation are chemical dyes and fragrances, soaps, some flower and spice oils, shaving creams, tanning lotions or spray tans, changes in temperature, excessive cleansing or exfoliating, waxing, threading, shaving and bleaching. People with sensitive skin should try to avoid products with unnecessary fragrances or dyes, and generally avoid using products that cause irritation. Sensitive skin is typically dry, but can be oily, normal or combination as well.