The face begins at the anterior hairline, stops at the ears, and is bounded by the lateral jawline and chin. It is the most complex and challenging area of the body for the formulator, yet more products are designed for facial use than any other. Why? Because the face is the purveyor of our image, our personality, our health, and our age. It identifies who we are, how we are, where we are, and sometimes what we hope to be. From a dermatologic standpoint, the face possesses unique medical attributes. It contains all of the glandular structures of the body, including hair, and is characterized by dry skin and transitional skin. The transitional skin is found around the eyes, nose, and mouth. It is also frequently afflicted by a variety of skin diseases that complicate product development.
Anatomy and Physiology
Let us begin by considering the anatomy and physiology of the face. The facial skin is the thinnest on the body, except for that around the eyelids. This means that the skin is easy to injure, but also readily healed. It is for this reason that skin surgeons prefer to operate on facial skin. Incisions heal imperceptibly due to the minimal movement of skin on the face and the fact that the face is not weight bearing. Compare the facial skin to that of the upper chest, which heals extremely poorly. The chest skin is constantly subject to pulling and pushing as the arms move, which predisposes any chest incision to healing with a thickened hypertrophic scar. Compare the facial skin to that of the lower ankles, which is some of the slowest healing skin on the body, because it must bear a load with walking accompanied by constant movement. Indeed, the facial skin is some of the most forgiving on the body when it comes to surgical manipulation.
On the other hand, the facial skin is some of the least forgiving when it comes to irritation and allergy. The thinness of the facial skin that is so desirable for healing purposes allows the ready penetration of irritants and allergens, making product formulation more challenging. The face is also characterized by numerous follicular structures in the form of pigmented terminal or full thickness hairs in the eyebrows, eyelashes, and male beard combined with white fine downy vellus hairs over the rest of the face. These follicular structures are the transition between the skin on the surface of the face and the ostia, or openings, that lead down into the follicle itself and the associated sebaceous or oil glands. The follicular ostia forms the structure that is commonly referred to as a pore. The follicle creates the interesting topography of the facial skin with mountains occurring around each follicular structure and intervening valleys in between. This unique topography is known as dermatoglyphics, which forms the pattern and texture of the skin. Prominent dermatoglyphics lead to what is termed coarse skin while a more even skin surface with smaller pores leads to fine skin and better texture.
At the base of the pore lies the hair follicle just below the oily sebaceous gland. The skin lining of the pore connecting the surface to the depth of the follicle is an important
transitional area. This is the skin that sloughs improperly creating the environment appropriate for acne. It is also the skin that is easily irritated resulting in the “breakouts” experienced following the use of products that cause the formation of red bumps, known as papules, and pus bumps, known as pustules. This skin cannot be reached by traditional cosmetics and skin care products, but irritant or allergic reactions that occur at the skin surface can impact this follicular lining.
The pore is not only connected to the hair, but also to the sebaceous gland. The sebaceous gland is the structure that produces sebum. Sebum is the oil of the body that lubricates the skin surface, but also provides a food supply for bacteria, such as Propioni – bacterium acnes, and fungal elements, such as pityrosporum species. The bacteria propionibacterium acnes digests the sebum releasing free fatty acids that initiate inflammation characterized by the influx of white blood cells. These white blood cells form the pus that is seen with acne. Pityrosporum species are responsible for the initiation of the inflammation, also due to the release of free fatty acids, which is associated with the onset of dandruff of the scalp and face. Dandruff of the face is medically termed seborrheic dermatitis.
The facial skin also contains two types of sweat glands, known as eccrine and apocrine glands. Eccrine glands are the sweat glands that produce a sterile watery liquid associated with the maintenance of body temperature. It is the evaporation of the sweat from the skin surface that allows excess heat to be rapidly removed from the body. However, on the face sweating can occur in response to emotion and the ingestion of spicy food. This type of sweating is under a different neural control than that associated with thermoregulation. The other type of sweat gland, known as an apocrine gland, produces a scented sweat that is unique to each individual. This apocrine sweat contributes to body odor and allows certain perfumes to smell differently on each individual. The apocrine sweat glands are uniquely located around the eyes.
Our discussion to this point has focused on the anatomic structures present on the facial skin to include pores (follicular ostia), terminal hairs, vellus hairs, sebaceous glands, eccrine glands, and apocrine glands. The face possesses a larger variety of these structures than any other skin on the body, which makes it unique. But, the skin on the face is structurally identical to any other skin on the body in that it is composed of two layers, to include the epidermis and the dermis. The epidermis is the outer layer of skin, which is covered by a thin layer of nonliving skin cells, known as the stratum corneum. The stratum corneum is the layer of skin with which all skin care products interact. It is this structure that is impacted by the majority of formulations concocted by the cosmetic chemist. Beneath the epidermis lies the dermis. The dermis is the collagen-rich, structurally strong layer of skin. It is the dermis of cow hides that is turned into leather. The dermis actively participates in the immunologic surveillance of the body and produces a scar if injured. For all practical purposes, the cosmetic chemist is not concerned with the dermis as this is the realm of prescription drugs.
The stratum corneum represents the skin barrier and is integral in differentiating those substances that must remain outside the body from those that are allowed to enter through the skin. It accomplishes this end by a unique arrangement of dehydrated skin cells, known as corneocytes, interspersed between a combination of oily substances, known as intercellular lipids. The intercellular lipids implicated in epidermal barrier function include sphingolipids, free sterols, and free fatty acidsa. This organization has been likened to a brick wall where the bricks are represented by the nonliving corneocytes
Elias PM: Lipids and the epidermal permeability barrier. Arch Dermatol Res 270:95-117, 1981.
and the mortar is represented by the intercellular lipids. Any disruption in this organization, either through removal of the coreneocytes or intercellular lipids, results in a barrier defect that can ultimately result in skin disease, our next topic of discussion.
Common Dermatologic Disease Considerations
The causes of most facial skin diseases that can be impacted by skin care products are due to barrier defects. The barrier defects are mostly due to removal of the intercellular lipids resulting in excessive water loss from the skin surface, a phenomenon known as transepidermal water loss. This loss of water from the skin produces dryness, known as xerosis, with the onset of flaking of the facial skin later accompanied by redness and swelling. These physical findings are associated with the subjective findings of tightness, itching, stinging, burning, and pain, in order of increasing skin disease severity. It is the onset of this transepidermal water loss that is necessary to initiate synthesis of intercellular lipids to allow barrier repairb, c.
The skin disease that results from dryness is known as eczema. Eczema is treated by creating an environment suitable for barrier repair to occur. Most dermatologists recommend decreased bathing and use of a mild detergent to prevent further undesirable removal of the intercellular lipids. They also recommend the use of oily moisturizers to create an artificial barrier soothing irritated nerve endings, thus preventing itching and pain, and to decrease transepidermal water loss. Moisturizers are used not to hydrate the skin, but rather to minimize further damage while the skin is healing the barrier endogenously.
It is worth mentioning that some individuals are more susceptible to barrier damage than others. For unknown reasons, some persons may have defective intercellular lipids, insufficient secretion of intercellular lipids, or corneocytes that are less resistant to structural damage. These persons will demonstrate barrier defects more readily than others and will have eczema that is harder to control and sometimes impossible to cure. These individuals are classified as possessing sensitive skin and are used in cosmetic testing panels for this reason.
The other common facial skin conditions of acne, acne rosacea, and seborrheic dermatitis are due to a completely different mechanism of action. They may ultimately result in a facial skin barrier defect, but can be considered diseases of the facial skin biofilm. The biofilm is that thin layer of sebum, eccrine sweat, apocrine sweat, skin care products, cosmetics, medications, environmental dirt, bacteria, and fungus that is present on the skin surface. A healthy biofilm will lead to skin health while biofilm abnormalities will ultimately lead to disease. For example, as has been mentioned previously, an overgrowth in the facial flora of propionibacterium acnes will lead to acne. Without propionibacterium acnes there can be no acne. Thus, skin care products can impact facial acne by minimizing the growth of this organism on the face. Propionibacterium acnes is also felt to be operative in an adult acne condition associated with facial redness and papules and pustules known as acne rosacea.
Seborrheic dermatitis is different from acne in that it is caused by a fungus, known as pityrosporum. This fungus is normally found on the facial skin in small numbers with its growth kept in check by the immune system. Seborrheic dermatitis, characterized as dandruff of the face, is more common in the elderly, persons with AIDS, after severe
b Jass HE, Elias PM: The living stratum corneum: implications for cosmetic formulation. Cosmet Toilet 106 October 1991:47-53.
c Holleran W, Feingold K, Man MQ, Gao W, Lee J, Elias PM: Regulation of epidermal sphingolipid synthesis by permeability barrier function. J Lipid Res 32:1151-1158, 1991.
medical illnesses, and following chemotherapy. Sometimes severe untreatable seborrheic dermatitis is the first indication that an immune problem may be present. Skin care products can dramatically affect the presence of fungal elements on the facial skin, thus minimizing or maximizing the chances of developing seborrheic dermatitis through proper hygiene, discussed next.
Hygiene Needs
The hygiene needs of the face are more complex than any body area, except for perhaps the genitalia. This is due to the interplay between the skin, the hair, the sebaceous glands, the eccrine glands, and the transitional skin around the eyes, nose, and mouth. The moist skin of the nasal mucosa and the oral mucosa is an environment perfect for bacterial colonization and growth. Bacteria from these sites can easily move onto the facial skin covered with a mixture of sebum and sweat perfect for encouraging bacterial growth and spreading infection. The presence of hair also provides added surface area for bacterial growth to occur, thus the facial skin is a common site of infection.
Good facial hygiene is a careful balance between maintaining a healthy biofilm while preserving the integrity of the barrier by leaving the intercellular lipids intact. This can be challenging in light of the fact that cleansers cannot accurately differentiate between sebum and intercellular lipids. It is further challenged by the ever changing sebum production of the facial glands, which varies by both age and climate, and the different bacteria with which the body comes in contact. Many dry complected individuals fail to clean the face due to the fear that dryness will result. Ultimately, disease results. Thus, facial skin must be kept clean, but not too clean.
Skin Care Needs
In many cases, barrier damage from meeting the hygiene needs of the skin must be balanced by the use of additional skin care products. Thus, the skin care needs of the face are influenced not only by the unique attributes of the facial skin, but also by the needs created through the use of other skin care products. What are the skin care needs of the face? They are the maintenance of skin health and the enhancement of skin beauty. These are two very different goals. The maintenance of skin health has already been discussed as optimization of the biofilm, which is a careful balance between cleansing (Chapter 4) and moisturizing (Chapters 6, 7). Yet, there are other skin needs. These include the creation of an even skin surface and the prevention and reversal of skin damage.
The image of healthy facial skin is shiny skin due to abundant light reflection. This light reflection is due to an even surface. Causes of uneven facial skin include scars, facial growths such as moles, skin disease such as acne, and retained dead skin cells from the stratum corneum, known as corneocytes. Little can be done cosmetically to affect facial scars and moles, while acne issues have already been discussed. One area that deserves further mention is the issue of retained corneocytes. During youth the corneocytes slough easily as the cellular message for cell disadhesion is well transmitted. With advancing age, the cells do not disadhese or desquamate as readily leading to retained dead skin scale. This skin scale, or dander, creates an uneven skin surface. This has led to the concept of exfoliation, which uses chemical or mechanical means to encourage the removal of the dead skin scale. Exfoliants (Chapter 15) are the product category addressing this need. Exfoliation through the use of mild acids in astringent formulations (Chapter 5), such as glycolic or lactic acid, or the use of abrasive scrubs or textured cleansing cloths removes the skin scale improving skin texture and skin shine.
The other major skin need is the prevention and reversal of skin damage from sun exposure. Sun contains UVB and UVA radiation, both of which damage the skin. This damage can be seen in the form of collagen loss resulting in premature skin wrinkling or abnormal pigmentation resulting in uneven skin color. Facial skin care products have been developed to meet these needs. Sunscreens (Chapter 9) are themost important anti-aging facial skin care products currently available for their ability to absorb, scatter, or reflect UVB and/or UVA radiation. After cleansing for good facial skin hygiene, sunscreen is the most important facial skin care product to maintain skin health. Unfortunately, sunscreen is not completely effective in preventing UV damage and compliance, especially during youth, is not 100%. Thus, skin lightening preparations (Chapters 13, 14) are available to even irregular pigmentation and antiaging products (Chapters 9, 10, 11, 12) attempt to reverse facial skin damage once it has occurred.