Care and Maintenance of Normal Skin

Falguni Asrani

Molly Wanner

The skin serves a variety of important functions including regulation, defense, and protection. The skin protects us from the elements: from wind, cold, heat, and ultraviolet (UV) light, and is a first line of defense again infection. It is an organ of temperature regulation, sensation, and excretion, and allows us to prevent water loss to the environment.

The efficacy of the skin barrier will affect skin’s ability to protect. Eczema patients have a deficiency of their skin barrier that makes them more susceptible to infection and inflammation. Although patients with normal skin may not have an internal predisposition to a poor skin barrier, the environment has external forces that influence the skin barrier. As a result, even normal skin requires care and maintenance.

This chapter will review the cleansing, moisturizing, and sun protection routine that normal skin requires. It will review how different environments create different needs, how skin through the years changes in its requirements, and it will present ways to protect and preserve the skin barrier.

Skin Barrier

The care and maintenance of normal skin begins with an understanding of the skin barrier. The skin’s barrier is at the outermost surface of the skin and is called the stratum corneum. The role of the stratum corneum is to prevent water loss, and minimizing water loss is crucial for normal skin functioning. Water and the water gradient within the stratum corneum drive the function of enzymes necessary for normal skin turnover. Internal and external conditions can affect the water-retaining ability of the stratum corneum, and routine skin care can enhance the efficacy of the stratum corneum.

The stratum corneum is comprised of skin cells and intercellular lipid material. These two components form the “brick and mortar” structure of the skin that surrounds and protects our internal organs. Inside the skin cells of the stratum corneum, there is a substance called the “natural moisturizing factor” (NMF) that in combination with intracellular lipids prevents water loss.

Skin Barrier Corneocytes

The bricks of the skin barrier are called the corneocytes of the stratum corneum. The corneocytes start as undifferentiated skin cells called keratinocytes in the basal layer of the epidermis; these are gradually pushed outward as they undergo changes ultimately designed to create the skin barrier that protects us. Corneocytes do not have intracellular organelles and rather, contain the NMF. Corneocytes are surrounded by a strong, protective shell
called the cornified cell envelope, which protects the corneocytes from mechanical damage, and are linked by corneodesmosomes, which hold the cells together.

The NMF is a potent attractor of water that keeps the skin hydrated, corneocytes plump and healthy, and the skin barrier tight and flexible. The NMF is also critical for creating the aqueous environment important for normal skin turnover or desquamation. The NMF draws water from the deeper layers of the skin and may draw water from the environment as well.

An insoluble protein called profilaggrin is dephosphorylated to form filaggrin, which is subsequently altered in the outmost layers of the skin to form the NMF. The NMF is comprised of amino acids, organic acids, urea, inorganic acids, and ions such as calcium and magnesium.

Skin Barrier Intercellular Lipids

The mortar of the skin barrier is comprised of ceramides, cholesterol, and free fatty acids. These lipids are bipolar, and when combined, form alternating hydrophilic and hydrophobic lipid bilayers. It is not only the presence of these lipids, but their ratios that determine the efficacy of the mortar. Cholesterol is thought to provide the structure and stabilize the bulk of the material, which is comprised of ceramides.

The strength of the skin barrier depends on the quantity and quality of the materials, and disease states such as atopic dermatitis or congenital disorders called ichthyoses are characterized by compromised building blocks. Patients with atopic dermatitis have been found to have mutations in filaggrin and low levels of ceramides, which in part explains the ineffective skin barrier seen in these patients.

Skin Barrier and the Environment

Even in patients with “normal” skin, a variety of exogenous factors can affect the skin barrier. Environmental conditions such as temperature, humidity, seasonal change, and UV light alter the skin barrier, with UV light being particularly harmful. Temperature, too hot or cold, but particularly too cold, can be problematic. Cold air holds less moisture than warm air and cold reduces the mobility and flexibility of the skin. Dry environments are not detrimental to the skin barrier, per se, as the skin will accommodate. However, shifting from a humid to a dry environment can delay barrier recovery. Thus, a patient who lives year-round in a dry climate like Arizona will have better barrier function than a patient who travels to different climates or who lives in an environment with seasonal changes from humid to dry.

Efforts to cleanse the skin can damage the skin barrier; even routine cleansing can remove much of the soluble NMF from the skin. Cleansing can also harm the skin barrier because many cleansers have a high pH, which triggers breakdown of the corneodesmosomes that hold corneocytes together. Aging decreases the NMF, and the skin barrier becomes less effective over time. Conditions of stress, which lead to elevated glucocorticoids or even medications that lower cholesterol, can alter the skin barrier. Thus, the care and maintenance of normal skin will vary with environmental conditions, the type of cleansing required, the age of the patient, and even medications.

Cleansers

Cleansing is accomplished using surfactants, which are molecules with hydrophilic and hydrophobic moieties. Surfactants such as sodium tallowate
and sodium cocoate are present in soap. Synthetic surfactants such as sodium cocoyl isethionate are used in synthetic cleansers, called syndets. These molecules remove dirt and bacteria from the skin, but also have the secondary effect of damaging the skin barrier. These secondary effects are due to alteration of the skin’s normal pH (5.5), alteration in ability of proteins in the skin to bind water after cleansing, a decrease of the NMF, damage to the lipid layers, or reduction of lipids in the skin.

The type of cleansing required depends on the amount of dirt and bacteria to remove as well as on environmental and patient characteristics. Aggressive surfactants may be needed to remove heavy dirt. On the other hand, in conditions of cool temperatures or low humidity, gentle cleansing is recommended. Gentle cleansing is also more appropriate in older patients who are predisposed to a less effective skin barrier.

Soaps such as Ivory or soap detergent combinations such as Irish Spring and Dial are alkaline lipid formulations with a pH of 9 to 10 that can effectively solubilize dirt or other materials from the skin. Because soaps are equally efficacious at stripping the natural lipids and moisturizers of the skin as well, soaps are best reserved when the removal of dirt, environmental pollutants, bacteria, or oil is required. Even glycerin-based transparent soaps, while milder, have an alkaline pH that can be irritating. If aggressive cleaning is needed, it should be used in combination with moisturizers to replace lost moisture to avoid damaging the skin barrier.

When heavy cleaning is not required, patients are advised to use gentle cleansers that are pH balanced similarly to the skin. These syndet cleansers, such as Dove, Olay, or Cetaphil have a pH of 5.5 to 7. Syndets are formulated using synthetic surfactants, most commonly sodium cocoyl isethionate. The formulation of a cleanser as a liquid, instead of a bar, may further facilitate gentle cleansing.

Liquid body washes are formulated either as a solution of surfactants or in some cases, in combination with emollients as a moisturizing wash. Moisturizing washes deposit lipids to protect the skin barrier during the cleansing process and are the mildest type of cleanser. Moisturizing cleansers are especially useful during the winter season for older patients.

Facial cleansers tend to have gentler ingredients than body washes and can be formulated as foaming or nonfoaming cleansers. Foaming cleansers use mild surfactants, while nonfoaming cleansers use emollient cleansers instead of surfactants and are the mildest of all. Nonfoaming cleansing lotions or milks can even be wiped off (instead of rinsed) to further enhance gentleness. Nonfoaming cleansers are best reserved for older patients. Foaming cleansers may be preferred by younger patients who may not like or need an emollient residue left on the skin after cleansing. Cleansers can be combined with materials to remove make-up as well.

Moisturizers

A moisturizer is necessary if the skin barrier has been altered through the normal aging process or via exogenous factors such as a cleansing routine. A moisturizer can repair the skin barrier and lead to decreased bacterial colonization. Recall that the skin barrier is formed by corneocytes filled with NMF and an intercellular lipid bilayer comprised of ceramides, cholesterol, and free fatty acids. Moisturizers simulate the NMF and/or the lipid bilayer to enhance skin barrier repair. Although moisturizers can hydrate the skin somewhat, moisturizers primarily function through prevention of water loss, which facilitates the body’s own barrier repair mechanisms.

The NMF is a potent attractor of water; the NMF corollary in moisturizers is called a humectant. Like the NMF, humectants such as glycerin, sorbitol,
urea, and alpha hydroxyl acids pull water into the outmost layer of the skin. 2-Pyrrolidone-5-carboxylic acid is reported to be a particularly effective humectant. Humectants such as alpha hydroxyl acids may also increase skin elasticity.

Ingredients that mimic the effects of the lipid bilayer are emollients and occlusives, which seal the skin and decrease water loss. Moisturizers can occlude the skin and/or interact with intercellular lipids in the stratum corneum to facilitate “moisture,” that is, water retention in the skin. Occlusives such as petrolatum, lanolin, mineral oil, dimethicone, beeswax, and silicone form an occlusive barrier to prevent water loss. Emollients such as cholesterol, squalene, and fatty acids fill in spaces between desquamating corneocytes to seal the skin. Physiologic lipids such as cholesterol, fatty acids, and ceramides penetrate to deeper layers of the skin, whereas petroleum only penetrates the very superficial layers of the stratum corneum.

Most moisturizers utilize a combination of humectants and emollients or occlusives. Creating an occlusive barrier is more effective in combination with a humectant to bring water to the stratum corneum. Using a humectant alone will draw water to the outer surface of the skin, which will be lost to the environment with an impaired barrier. However, moisturizers without humectants may also make skin more susceptible to irritation.

The ingredients of a moisturizer and the proportions of these ingredients can affect outcome. A study of the effect of moisturizer use on normal skin showed that moisturizers can increase or decrease transepidermal water loss depending on the components of the moisturizer. When physiologic lipids of the skin barrier (cholesterol, ceramides, and fatty acids) are used as emollients, all three components must be present, or barrier repair is impaired. Moisturizers can also be created with a positive (cationic), negative (anionic), or neutral charge. A cationic lotion can bind to the slightly negative keratin proteins in the stratum corneum and may offer long-lasting moisture.

Moisturizers can be formulated as creams, lotions, ointments, oils, pastes, and gels. In a simple classification, moisturizers can be described as oil-in-water emulsions (lotions); water-in-oil emulsions (creams); or oil-only moisturizers (petrolatum). A more detailed description of moisturizer formulations has been described elsewhere (Chapter 2). In general, creams (water-in-oil emulsions) provide more effective hydration than oil-in-water emulsions; however, patients often prefer oil-in-water lotions for ease of application.

In terms of efficacy, petroleum jelly is the most effective moisturizer and reduces transepidermal water loss by 99%, followed by creams, and then lotions. Lotions are best suited for use in the summer. Lotions may not provide enough moisture during the winter, particularly in climates characterized by low humidity and low temperatures. Traveling on airplanes in low-humidity environments or from humid to dry places may require the use of a cream. For older patients, who have less natural moisturizer in the skin and may be on cholesterol-lowering agents, petroleum jelly may be necessary. The aggressiveness of the cleansing routine will also influence the type of moisturizer required.

Sun Protection

Sunlight emits mainly infrared, visible, and ultraviolet (UV) light, although other wavelengths are also present. Consisting of UVA (315 to 400 nm), UVB (280 to 315 nm), and UVC (100 to 280 nm), ultraviolet radiation is instrumental in the development of skin cancer and photoaging. UVA comprises the majority of UV light, about 96.5%, reaching the earth. UVB represents the remainder as UVC is absorbed by the ozone layer. UV light in general is affected by geographical location on the earth, time of day, and weather conditions, although UVA light, in particular, is affected less so than other wavelengths.

Table 4-1 American Academy of Dermatology Be Sun Smart^SM Guidelines

Generously apply a broad-spectrum, water-resistant sunscreen with a sun protection factor (SPF) of at least 15 to all exposed skin. “Broad-spectrum” provides protection from both ultraviolet A (UVA) and ultraviolet B (UVB) rays. Reapply approximately every 2 hours, even on cloudy days, and after swimming or sweating.
Wear protective clothing, such as a long-sleeved shirt, pants, a wide-brimmed hat, and sunglasses, where possible.
Seek shade when appropriate, remembering that the sun’s rays are strongest between 10 AM and 4 PM. If your shadow is shorter than you are, seek shade.
Protect children from sun exposure by playing in the shade, using protective clothing and applying sunscreen.
Use extra caution near water, snow, and sand as they reflect the damaging rays of the sun, which can increase your chance of sunburn.
Get vitamin D safely through a healthy diet that may include vitamin supplements. Don’t seek the sun.
Avoid tanning beds. Ultraviolet light from the sun and tanning beds can cause skin cancer and wrinkling. If you want to look like you’ve been in the sun, consider using a sunless self-tanning product, but continue to use sunscreen with it.
Check your birthday suit on your birthday. If you notice anything changing, growing, or bleeding on your skin, see a dermatologist. Skin cancer is very treatable when caught early.