What causes dry skin and what works for skin moisturizing?
Dry skin is caused by two factors: (I) Damage to the skin’s protective barrier which yields excessive water loss through the skin, and (II) An important reduction in the concentration of the skin’s water-holding sugar and protein molecules, the complex proteoglycans and glycosaminoglycans (GAGs) molecules.
Many skin moisturizers and emollient products sold by the major skin care companies delay the healing of irritated and damaged skin and make the situation worse by inhibiting natural skin repair. New instruments that allow to screen what goes on and inside the skin have demonstrated that most popular moisturizers increase skin damage in ways similar to skin irritants. Creams that claim to “retain” water by creating an occluding barrier on the surface of the skin such as those creams containing waxes, oils, petrolatum and lanolin are also not the right answer for skin dryness. Cosmetic moisturizers loosen the skin’s protective barrier and hydrate (wet) the skin proteins but have the long-term effect of damaging the skin.
Most if not all the popular moisturizers and emollients currently sold by the major skin care brands contain high concentrations of detergents and detergent-like chemicals, despite many years of sound evidence that such detergents degrade the skin’s natural protective function and damage the skin. Also, many of the dyes and optical diffusers used to give the appearance of healthy skin are damaging to skin as they react and create free radicals that damage healthy cells.
What is needed to protect the skin surface, and to restore the capacity of the skin to remain hydrated from within, is to help the skin be in a situation in which normal skin renewal and repair can occur.
Understanding how skin is constructed can help you better care for your skin
Beautiful, healthy skin is determined by how healthy are its structures and how properly the components within the skin function. To maintain beautiful skin, and slow the rate at which it ages, the structures and functions of the skin must be supplemented and protected. In order to know how to supplement and protect the skin, it’s important to know more about the skin’s basic anatomy and composition.
There are three major components of the skin. At the base is the hypodermis, which is subcutaneous fat (just beneath the surface) that functions as insulation and padding for the body. Next is the dermis, which provides structure and support. On the top outer layer is the epidermis, which functions as a protective shield for the body.
Natural lipids and fats in our skin provide the epidermal barrier to transcutaneous water loss. These lipids in the upper skin area called the stratum corneum are arranged in layers called lamellae. The lower skin layers contain more typical fats such as triglycerides and phospholipids while the upper layers have more ceramides, cholesterol and free fatty acids.
Hypodermis
The hypodermis is the deepest section of the skin. The hypodermis refers to the fat tissue below the dermis that insulates the body from cold temperatures and provides shock absorption. Fat cells of the hypodermis also store nutrients and energy. The hypodermis is the thickest in the buttocks, palms of the hands, and soles of the feet. As we age, the hypodermis begins to atrophy, contributing to the thinning of aging skin.
Dermis
The dermis is located between the hypodermis and the epidermis. It is a fibrous network of tissue that provides structure and resilience to the skin. While dermal thickness varies, it is on average about 2 mm thick.
The major components of the dermis work together as a network. This mesh-like network is composed of structural proteins (collagen and elastin), blood and lymph vessels, and specialized cells called mast cells and fibroblasts. These are surrounded by a gel-like substance called the ground substance, composed mostly of glycosaminoglycans. The ground substance plays a critical role in the hydration and moisture levels within the skin.
The most common structural component within the dermis is the protein collagen. It forms a mesh-like framework that gives the skin strength and flexibility. The glycosaminoglycans—moisture binding molecules—enable collagen fibers to retain water and provide moisture to the epidermis. Another protein found throughout the dermis is the coil-like protein, elastin, which gives the skin its ability to return to its original shape after stretching. In other words, elastin provides the skin with its elasticity.
Both collagen and elastin proteins are produced in specialized cells called fibroblasts, located mostly in the upper edge of the dermis bordering the epidermis.
Intertwined throughout the dermis are blood vessels, lymph vessels, nerves, and mast cells. Mast cells are specialized cells that play an important role in triggering the skin’s inflammatory response to invading microorganisms, allergens, and physical injury.
The blood vessels in the dermis help in thermoregulation of the body by constricting or dilating to conserve or release heat. They also aid in immune function and provide oxygen and nutrients to the lower layers of the epidermis. These blood vessels do not extend into the epidermis. Nourishment that diffuses into the epidermis only reaches the very bottom layers. The cells in the upper layers of the epidermis are dead because they do not receive oxygen and nutrients.
The junction between the dermis and epidermis is a wave-like border that provides an increased surface area for the exchange of oxygen and nutrients between the two sections. Along this junction are projections called dermal papillae. As you age, your dermal papillae tend to flatten, decreasing the flow of oxygen and nutrients to the epidermis.
Epidermis
The epidermis is the outermost layer of the skin. Categorized into five horizontal layers, the epidermis actually consists of anywhere between 50 cell layers (in thin areas) to 100 cell layers (in thick areas). The average epidermal thickness is 0.1 millimeters, which is about the thickness of one sheet of paper. The epidermis acts as a protective shield for the body and totally renews itself approximately every 28 days.
The first layer of the epidermis is the stratum basale. This is the deepest layer of the epidermis and sits directly on top of the dermis. It is a single layer of cube-shaped cells. New epidermal skin cells, called keratinocytes, are formed in this layer through cell division to replace those shed continuously from the upper layers of the epidermis. This regenerative process is called skin cell renewal. As we age, the rate of cell renewal decreases. Melanocytes, found in the stratum basale, are responsible for the production of skin pigment, or melanin. Melanocytes transfer the melanin to nearby keratinocytes that will eventually migrate to the surface of the skin. Melanin is photoprotective: it helps protect the skin against ultraviolet radiation (sun exposure).
The second layer of the epidermis is the stratum spinosum, or the prickle-cell layer. The stratum spinosum is composed of 8-10 layers of polygonal (many sided) keratinocytes. In this layer, keratinocytes are beginning to become somewhat flattened.
The third layer is called the stratum granulosum, or the granular layer. It is composed of 3-5 layers of flattened keratin—a tough, fibrous protein that gives skin its protective properties. Cells in this layer are too far from the dermis to receive nutrients through diffusion, so they begin to die.
The fourth layer in the epidermis is called the stratum lucidum, or the clear layer. This layer is present only in the fingertips, palms, and soles of the feet. It is 3-5 layers of extremely flattened cells.
The fifth layer, or horny layer, is called the stratum corneum. This is the top, outermost layer of the epidermis and is 25-30 layers of flattened, dead keratinocytes. This layer is the real protective layer of the skin. Keratinocytes in the stratum corneum are continuously shed by friction and replaced by the cells formed in the deeper sections of the epidermis. In between the keratinocytes in the stratum corneum are epidermal lipids (ceramides, fatty acids, and lipids) that act as a cement (or mortar) between the skin cells (bricks). This combination of keratinocytes with interspersed epidermal lipids (brick and mortar) forms a waterproof moisture barrier that minimizes transepidermal water loss (TEWL) to keep moisture in the skin. This moisture barrier protects against invading microorganisms, chemical irritants, and allergens. If the integrity of the moisture barrier is compromised, the skin will become vulnerable to dryness, itching, redness, stinging, and other skin care concerns.
In the very outer layers of the stratum corneum, the moisture barrier has a slightly acidic pH (4.5 to 6.5). These slightly acidic layers of the moisture barrier are called the acid mantle. The acidity is due to a combination of secretions from the sebaceous and sweat glands. The acid mantle functions to inhibit the growth of harmful bacteria and fungi. The acidity also helps maintain the hardness of keratin proteins, keeping them tightly bound together. If the skin’s surface is alkaline, keratin fibers loosen and soften, losing their protective properties. When the pH of the acid mantle is disrupted (becomes alkaline)—a side effect of common soaps—the skin becomes prone to infection, dehydration, roughness, irritation, and noticeable flaking.
A number of components are common to both the dermis and epidermis. These are: pores, hair, sebaceous glands, and sweat glands.
Pores are formed by a folding-in of the epidermis into the dermis. The skin cells that line the pore (keratinocytes) are continuously shed, just like the cells of the epidermis at the top of the skin. The keratinocytes being shed from the lining of the pore can mix with sebum and clog the pore. This is the precursor to acne. If oil builds up inside pores, or if tissue surrounding the pore becomes agitated, pores may appear larger.
Hair grows out of the pores and is composed of dead cells filled with keratin proteins. At the base of each hair is a bulb-like follicle that divides to produce new cells. The follicle is nourished by tiny blood vessels and glands. Hair prevents heat loss and helps protect the epidermis from minor abrasions and exposure to the sun’s rays.
Sebaceous glands are usually connected to hair follicles and secrete sebum to help lubricate the follicle as it grows. Sebum also contributes to the lipids and fatty acids within the moisture barrier. Oil production within the sebaceous gland is regulated by androgen levels (hormones such as testosterone).
Sweat glands are long, coiled, hollow tubes of cells. The coiled section is where sweat is produced, and the long portion is a duct that connects the gland to the pore opening on the skin’s surface. Perspiration excreted by the sweat glands helps cool the body, hydrate the skin, eliminate some toxins (i.e., salt), and maintain the acid mantle.
