Transepidermal water loss is the quantity of water that passes from inside the skin to the surrounding atmosphere. Moreover, damage to the skin through injury, infection, burns, and other assaults will impair the normal functioning of the epidermis and its ability to retain a good water balance.

A GLOBAL OBSERVATION
Approximately 71 percent of the Earth's surface is covered with water and 96.5 percent of that water is found in the ocean. The balance of percentage exists in the air as water vapor and in lakes, rivers, icecaps, glaciers, ground aquifers, plants, humans, and animals.

UNDERSTANDING HUMIDITY
Humidity can be measured in several ways, the most common of which is relative humidity. The physics of absolute humidity states that the hotter the air is, the more water it can contain. In other words, when there is 100 percent relative humidity, the air is completely saturated with water vapor and cannot hold any more. During times of high humidity, people feel like the temperature is hotter than it actually is because their sweat will not evaporate. The higher the humidity, the more uncomfortable people are due to the fact that their body cannot cool down. Conversely, when humidity is lower, people feel cooler because their body is able to maintain its appropriate temperature. Clouds are water vapor that has condensed as a result of warm air rising from the earth. They form to equalize the temperatures in the air.

WATER AND DEHYDRATION
The World Health Organization defines dehydration as "the condition that results from excessive loss of body water."1 It is a negative state of fluid imbalances, many of which are caused by disease. In severe cases of acute malnutrition, dehydration is caused by untreated diarrheal disease that leads to the loss of water and electrolytes. A cycle of severe malnutrition, combined with poor sanitation, points to diarrheal conditions that manifest into a continuum of health issues that become incessantly difficult to manage. Worldwide, there are approximately 1 billion people who do not have access to clean water and millions more are deprived of proper nutrients and adequate sanitation. Moreover, there are approximately 1.5 million children who die each year due to this succession of devastating life circumstances.

Conversely, more developed countries may portray safer living standards, including consistent clean water, sanitation, nutrition, and disease
management. No matter where one lives, however, the condition of dehydration has no boundaries. The importance of requisite water intake comes to the forefront in the prevention and/or management of disease.

THE HUMAN BODY
An adult's body contains about 60 to 75 percent water; an infant's body contains approximately 78 percent water, but eventually decreases to about 65 percent in the first year of life. Adult men have a water content of about 60 percent. Fatty tissue does not have as much water as lean tissue, thus adult women tend to have a water content of about 55 percent.2 Nevertheless, not all individuals who have more fatty tissue have as much water within their body. Living species' dependency on water for existence has not changed over thousands of years. Regardless where one resides, that requirement remains constant.

Water plays two essential roles for all living matter: It is life-giving and life-sustaining. Water is a fundamental nutrient to the life of every cell and serves as an essential building material. It is an internal regulator for body temperature through sweating and respiration and acts as a metabolic transport system for proteins and carbohydrates. The foods people consume become the products of energy conversion from the initial electrical energy-
generating property of water.

Water is the central regulator of energy and osmotic balance in the body and acts as a solvent for solutes during the regulation of all body functions. It regulates water-dependent chemical reactions (hydrolysis), drives chemical reactions within the cells, and is a primary driving force and source of
adenosine triphosphate.

Water acts as a shock absorber for the brain, spinal cord, and fetus. It is required for saliva, lubricates joints, and assists in flushing waste through urination. It is necessary for enzymatic activity of DNA and RNA structures of the nucleus of cells as well as repair. It acts as an adhesive material in the bondage of the cell architecture. Furthermore, the efficiency of neurotransmission systems depends on the availability of free and unengaged water in nerve pathways throughout the tissues. Water also increases the efficiency of red blood cells in the collection of oxygen in the lungs and helps reduce the risk of heart attacks and strokes.

All body functions are monitored and dependent upon the efficient flow of water. Transport of elements, hormones, chemical messengers, and nutrients all rely on adequate water levels.

WATER REGULATION THROUGHOUT LIFE PHASES
Stage one occurs during the life of the fetus in uterine. Adequate water during this phase is supplied by the mother's intake. Stage two transpires between the ages of 18 and 25, when the full height of the child has been achieved. Stage three takes place throughout early adulthood until death. A prerequisite
for healthy aging is homeostasis of fluid balance.

The body redistributes and regulates all available water. Water plays an essential hydrolytic role in all aspects of body metabolism. There are water-
dependent chemical reactions known as hydrolysis. Osmotic flow through the cell membrane generates hydroelectric energy through a voltage gradient, where it is stored in energy pools in the form of adenosine triphosphate. During times of persistent dehydration, a threshold is reached whereby the internal water supply becomes inadequate for cell activity, leading to volume loss inside and outside the cell. It is important to pay attention to signs of dehydration and not ignore thirst or other indicators, especially during illness onset, inflammation, and medicine consumption. Many illnesses become exacerbated when there is inadequate water intake. Relief of back and joint pain, migraine headaches, and stress all require adequate water intake in order to facilitate the metabolic chemicals and activity required for healing.

The elderly, as they are vulnerable to dehydration, must be especially vigilant about their water intake. Studies have shown an association between dehydration and mental function, as well as blood clot complication, infectious diseases, kidney stones, and constipation.3

THE ROLE OF WATER MOVEMENT WITHIN SKIN TISSUE
All cellular functions within the skin are dependent upon adequate water supply. The amount of internal water is significant to the health and function of the dermis and epidermis. Water is important to the secretory systems that are found within the skin, such as acid mantle, epidermal lipids, natural moisturizing factors, sebaceous glands, glycosaminoglycans, and circulatory systems.

All tissue must maintain sufficient water balance for the ability to function properly, including adjusting within one's environment. Balanced hydration is based on relevant ambient humidity, the retention power of the stratum corneum, the amount of water transmitted from the inner to the outer layers of the skin, and the length of time it takes water to move from the lower skin layers to the upper regions of the stratum corneum.

RELEVANT AMBIENT HUMIDITY
Skin hydration depends on a functioning natural moisture factor, the skin barrier, and balanced sebum. A person's skin continuously adjusts between outside atmospheric conditions and the temperatures maintained inside their home and workplace. For example, in arid regions, such as high desert or mountainous and tropical regions, the skin transitions with atmospheric changes in order to maintain its natural moisture levels. Extreme changes of relative humidity may begin to stress the skin, causing it to have difficulty maintaining internal moisture levels. Air conditioning and heating systems change indoor atmospheric humidity. These transitions can easily become stressors as the skin continuously adjusts between inside and outside atmospheric conditions. In dry conditions, transepidermal water loss is much greater. It stands to reason that facial moisturizers may not be as efficient when there is very low humidity since there is a characteristic threshold for every moisturizer. It becomes inefficient and releases the moisture in the surrounding air.

As the keratinocytes migrate upward from the spinosum layer into the granular layers, their cellular contents begin to transform into hardened filaments (keratohyalin structures), making the cells less flexible. The granular layer is vital for synthesizing material for the stratum corneum. Cells at this layer produce membrane-coating lamellar granules called odlund bodies that contain lipids and proteins. The lipid mixtures in the lamellar granules are made up of ceramides, cholesterol, free fatty acids, and cholesterol sulfate. They are dedicated lipid-rich apparatuses that extrude their lipidic and enzymatic contents through the keratinocyte cell membrane out into the extracellular spaces where they come in contact with the water. The lipids then form two layers – one of oil and the other of water – and are reorganized into multiple long sheets of lamellar structures. These structures play a dynamic role in barrier defense and controlling transepidermal water flow and maintaining proper hydration levels within the epidermis.

The epidermal tissue must remain as impermeable as possible with the exception of allowing enough water to maintain hydration at the outer layers of the stratum corneum, as well as supporting the enzymatic processes that facilitate corneo-desmosomal degradation and desquamation. The water content supports skin flexibility and the ability to adjust to relative internal and external humidity. The ability for the stratum corneum to maintain its water content is dependent upon the thickness of the stratum corneum, the organizational and compacting characteristics of the corneocytes that allow them to function properly, and the presence of very hygroscopic compounds largely found within the corneocytes.

QUALITIES OF THE NATURAL MOISTURIZING FACTORS

The natural moisturizing factors found in the skin are composed primarily of amino acids, pyrrolidone carbonic acid, and other compounds. The hygroscopic properties of natural moisturizing factors greatly contribute to the corneocytes' ability retain moisture. Natural moisturizing factors also facilitate enzymatic processes, including the dissolution of the desmosomes. Natural moisturizing factors consist of amino acids that are not only responsible for the moisture content of the skin, but also for its osmolytic balance. Furthermore, the amino acids and the urea of the natural moisturizing factors protect against reactive oxygen species.

ANTIOXIDANT SYSTEMS
The skin has a network of enzymatic and non-enzymatic antioxidant systems that help combat oxidative injury from pollution, bacteria, ultraviolet rays, microorganisms, or chemical oxidants. The normal functioning of these systems is reliant upon a balance of lipid and protein systems that maintain the barrier function and are essential for the skin to hold moisture. When there is oxidative stress within the lipid and protein structures of the cells, it degrades the barrier integrity. The skin begins to show signs of dryness with the increased water loss.

CARING FOR THE SKIN BARRIER
The stratum corneum contains signal functions that influence important controls within the epidermal layers. The horny layer has a direct influence on the regenerating process in the deeper layers of the skin. The normal function of the skin barrier declines with age, including lipid synthesis and the pH of the acid mantle. Choosing correct products for protecting the barrier is based on several factors, especially the client's age, lifestyle, and extent of accumulated damage. Many cosmetic products actually can interfere with the natural transepidermal water loss process. Mineral oils and silicones form too much of an impermeable film on the skin and can easily cause a lower transepidermal water loss that actually slows down the regeneration process.

The client ends up experiencing dry skin upon discontinued use of these substances. The perplexity of this situation is compounded since there was not a clear understanding that the skin barrier began to experience disorder and lost its ability to regenerate with the use of inappropriate cosmetic or dermatological products. Moreover, the prescribing of corticosteroids for inflammation provides a temporary relief, however, they actually contribute to increased skin sensitivity and deterioration of the condition.

The topic of dehydration expands in the attempt to define it. It is essential to understand the seriousness of consuming an adequate amount of water on a daily basis. How much is enough? According to the Institute of Medicine, men are advised to drink 13 cups a day (three liters) and women around nine cups (2.2 liters).4 Have clients check with their healthcare
professional for their particular requirements.

References
1 Dorland, W. A. (2007). Dorland's illustrated medical dictionary. Philadelphia, PA: Saunders.
2 Water properties: The water in you (Water Science School). (n.d.). Retrieved from https://water.usgs.gov/edu/propertyyou.html
3 MCFaes, MD, MSc, et al. (2017) Dehydration in Geriatrics. Retrieved from http://www.medscape.com/viewarticle/567678
4 Mayo Clinic Staff. (2014, September 5). Water: How much should you drink every day? Retrieved from http://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/water/art-20044256

Alexandra J. Zani is an international educator, researcher, and author with a background in cell biology and medical. Her passion for education resulted in receiving numerous advanced certifications, both in the United States and abroad. Zani earned an instructor license for aesthetics/cosmetology, is NCEA certified, certified in Oncology Esthetics®, and the Pastiche Method® of Skin Analysis. She is a member of the International Association for Applied Corneotherapy (IAC). Zani presents education for advanced aesthetic technology, including microcurrents, LED, and non-ablative laser. She is a specialist in the anti-aging sciences, including the effects of nutrition, lifestyle, and the mind/body connection.