It is accepted that wrinkles are a sign of cutaneous aging, appearing on sun-exposed areas, called actinic aging. These wrinkles appear most frequently on the face and the hands, and generally increase in both size and frequency as we age. Wrinkles typically form in areas of muscle contraction perpendicular to the long axis of the muscle. For example, as the frontalis muscle elevates when the eyebrow is raised, the lines will form across the forehead. Obicularis oculi muscles run in a circular fashion around the eye, and contraction of these results in crow’s feet. For a wrinkle to form, changes must occur in the epidermis, which becomes thinner with aging. This thinning is more noticeable at the deepest portion of the wrinkle. The dermoepidermal junction (DEJ) becomes flatter during aging, as the papillary structure often disappears. This flattening process, along with the reduction of the collagen Types I, III, IV, and IV, appears to be a key factor in the formation of wrinkles. Many small wrinkles form naturally and are related to contraction of muscles, and small changes in proteins in the skin, but large wrinkles are a sign of serious skin damage. Both internal and external causes are capable of damaging the skin.

External Causes Appear More Deleterious
In 2001 Jean-Luc Contet-Audonneau et al. published an interesting paper, one of the relatively few published research papers on the structure of wrinkles, outlining some specific proteins that are characteristic in wrinkled skin. Everyone knows what a wrinkle looks like, but it is extremely hard to define it anatomically, even more so biochemically. In order to understand the genesis and structure of wrinkles, we must first define some of the key proteins in the skin.
Desmosomes are intercellular junctions that tightly link adjacent cells. Filaggrin is a filament-associated protein that binds to keratin fibers in epithelial cells. It is an essential protein for the homeostasis of the epidermis. Keratohyalin is a protein structure found in granules in the stratum granulosum of the epidermis, which is involved in keratinization. Oxytalan fibers are thin elastic fibers that run perpendicularly to the epidermis. The reader will be familiar with collagen and elastin and glycosaminoglycan.
The DEJ becomes flatter during aging and the papillary structure often disappears. This flattening process, along with the reduction of the collagen VII, appear to be important factors in the formation of wrinkles. The dermis and hypodermis start to atrophy during aging as production of collagen is reduced. In addition, certain glycosaminoglycans (GAG) and the adipose tissue of the hypodermis lessen as production decreases. The key concept is that reduction of support structures is the basis of wrinkle formation. Consider if the foundation of a house were to collapse. Floors above and the roof would collapse into the basement. The same thing happens when a wrinkle forms. A mystery in wrinkle formation is the protein elastin. Thin elastic fibers known as oxytalan fibers are mainly composed of elastin and two glycoproteins, fibrillin and microfibril, (and associated glycoprotein (MAGP)) start to disappear in the sub-epidermis and in the dermis with wrinkle formation.

Some Observations and Histological Changes
As stated above, the thickness of epidermis stratum spinosum is generally thinner at the bottom of the wrinkle than on the wrinkles’ flanks. Examination of the skin histological preparation shows this: The desmoplakins reduction proves that epidermis thickness corresponds to reduction of the number of cellular layers. Even in the presence of this reduced epidermis, the stratum corneum of the wrinkle is often thickened by an accumulation of corneocytes that form a hard, horny plug. Along with this finding, keratohyalin granules are more abundant on the flanks of the wrinkle and less numerous at the bottom of the same wrinkle. In the dermis, collagen atrophy is more marked under the wrinkle. The elastic tissue is strongly modified in zones exposed to actinic radiation characterized by voluminous masses of elastotic tissue, resulting in forming pads on each side of the wrinkle. The GAG chondroitin sulphates modified with age and solar irradiation, (chondroitin sulphates in particular) strongly decreased under the bottom of the wrinkle in comparison with the control non-exposed zones.

Sleep Lines
Sleep lines are temporary wrinkles induced by pressure and moisture retention during sleep. The facial skin creates approximately 15 to 30 milliliters of water in the course of the night, which often is absorbed by the cotton pillowcase. The retained water essentially glues the epidermis to the pillowcase, while it also dissolves the keratin protein of the stratum corneum. In a very real sense, the face is microscopically stuck to the fabric of the pillowcase, so normal sleep movements actually pull the skin up and down or sideways, a force which signals the skin to produce collagenase. This same signal mechanism is helpful during a pregnancy, for example, when the downward pull of the growing abdomen signals the release of collagenase to help the skin expand to accommodate a growing baby. In addition, the retained water from nocturnal transepidermal water loss (TEWL) on a cotton or silk pillowcase can further cause dissolution of collagen fibers. The combined cotton and water on the skin results in a linear force that induces the formation of collagenase, the enzyme responsible for collagen destruction. The net result is that wrinkles form when sleeping on one’s side.
What can be done to remedy a situation that happens when the client is fast asleep? No topical treatment can overcome the physics of the errant forces that release collagenase. One successful remedy is to exchange the woven cotton or silk pillowcase to an engineered pillowcase that reduces TEWL, and is constructed from a knitted material where the fibers are upright and serve to provide direct stimulation to the cells. As every massage therapist knows, massage is effective because it puts a perpendicular force on the skin, and this signals the skin to produce collagen. The technology of functional fabrics as an adjunct to topical treatments is clearly the wave of the future, and the simple act of changing one’s pillowcase is proving to be very effective in preventing this type of damage.