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Have we been misinformed about water and skin health?

May 2, 2023

Did you know that water accounts for 50–80% of body weight, depending on lean body mass?

We all know that skin is a multilayer interface between you and the environment.

  • functioning for temperature regulation water transport
  • sensation
  • protection from external triggers and other barrier functions.

Water is an essential nutrient with multiple vital roles in skin physiology. Yet, while many myths abound, the optimal methods and amounts for hydrating the cellular and molecular skin requirements still remain elusive. 

Excluding perspiration, the average water turnover is approximately 4% of total body weight in adults. In a 70 kg adult, this is equivalent to 2,500–3,000 mL/day (National Health and Medical Research Council (2006; updated 2017, p.45).

Multiple principal factors influence the diversity of skin characteristics, along with causes and possible consequences. Primary among the elements are the various barriers and hydration of the integumentary system, specifically in the epidermis.

Water is essential for skin health and normal physiological functioning, yet our understanding of how much water is needed is limited.

Epidermal or Dermal

Cutaneous water content has essential roles in varying skin functions, such as the barrier function or the “envelope” function, and water deficiency is associated with several dermatological dysfunctions.

  • Skin connective tissue is crucial for water storage in the body.
  • Someone weighing about 70 kg has a skin tissue volume of about 7 litres.
  • The extracellular matrix comprises two-thirds of this volume and about 50% fluid with proteoglycans, binding one-third of the total interstitial fluid.

Getting and keeping water in the area is a delicate interplay of various pressures and mechanisms under the Starling Equation.

Water retention in the Stratum Corneum depends on two major components

  • natural hygroscopic agents within the corneocytes (collectively referred to as natural moisturising factor)
  • intercellular lipids are orderly arranged to form a barrier to transepidermal water loss (TEWL).

In the dermis, the high molecular weight glycosaminoglycan with markedly hydrophilic properties, hyaluronic acid (HA), contributes to the skin’s hydration and plastic properties.

How much water is needed?

One big myth related to the often quoted for healthy skin is drinking eight glasses of water a day.

The question has always been – how big is the glass?

  • Eight glasses a day for skin health is a major misquote from an advisory from the Mayo Clinic in New York, stating that 8, 8 oz glasses per day is recommended for healthy body fluid intake (body, not the skin).
  • However, this has since been withdrawn as no scientific evidence existed with the present information from the Mayo Clinic.

Further studies concluded that there is no basis to support the eight glasses of 8 oz per day intake with specific research needed to hydrate the skin maximally. Such is unlikely due to the differing requirements of each client.

Unfortunately, one study (Williams et al., 2007) relating to the effect of long-term [4 weeks] water intake [2.25 litres daily of mineral water or tap water] on skin physiology has been misquoted as showing significant improvement.

  • Ninety-three subjects drank 2.5 L of water a day (either tap or mineral water).
  • After four weeks, the measurements in the mineral water group revealed a significant decrease in skin density and increased skin thickness.
  • However, this was significant only in the participants who routinely drank comparably little before the study. Skin density increased significantly, and skin thickness decreased significantly in the tap water group, but not in the other group.
  • All measurements were on the volar forearm, with 86 subjects completing the study.

Objective skin surface morphology did not change in any group, which is interesting and important. Generally, drinking lots of water is believed to reduce the visible signs of cutaneous ageing, such as wrinkles and lines. This was not found in this study.

As the authors admitted, “…not all of the objectively measured changes can be explained straightforwardly, as the exact mechanisms necessitate further research in this area.” (Williams et al., 2007, p 136).

More recent studies

  • Later studies with more precise and technical analysis have provided more detail and concluded that water hydration improves skin health.
  • Regarding epidermal hydration, Palma et al. (2015) found a consistent improvement of superficial and deep hydration, although with different magnitudes in a group with lower initial water consumption (significantly greater and present in all anatomical areas), relative to the reduced impact observed in the group with adequate average water intake (p. 417).
  • Akdeniz et al. (2018) undertook a systematic review of 23 published articles, which indicated a slight increase in stratum corneum and “deep” skin hydration was observed after additional water intake.
  • Reductions in clinical signs of dryness and roughness were observed. The extensibility and elasticity of the skin increased slightly.

However, this appeared particularly in individuals with lower prior water consumption than those deemed with adequate water intake. Ultimately the authors declared the evidence weak in quantity and methodological quality.

Intake

Adequate water intake is entirely individual, depending on:

  • activity
  • climate
  • diet
  • metabolism
  • water quality
  • air conditioning, and health status.

Don’t think drinking as much water as you can daily is a great idea either – such can cause water poisoning (also referred to as water intoxication), causing cellular swelling (hyponatremia) and death if very high volumes are consumed.

There is no question you need water intake daily, yet how much remains elusive as a generalisation – your own body can tell you the amount you need.

  • It is often said that you drink when you’re thirsty, yet this is not so accurate a measure as you would already be dehydrated if you feel thirsty.
  • The World Health Organization (WHO) guidelines recommend 2.9 L per day for males and 2.2 L for females to maintain hydration, assuming average sedentary adults under average conditions.
  • Australian and New Zealand recommended intake is 3.4 litres per day for males, with adult females 2.8 litres per day (National Health and Medical Research Council, 2016, p.47).

While it is intuitive to think that increasing water intake would increase skin water values, this seems to be substantiated by science, even if the quality of the evidence is scientifically weak.

  • If the client has adequate water intake from whatever means, it appears they do not need to increase water intake for skin health. On the other hand, those who have less than ideal water intake, do need to increase water intake for skin health.
  • Remembering some of your treatments will affect the water composition of the skin, you need to consistently advise clients regarding adequate higher consumption of plain drinking water and, no doubt, lower consumption of other discretionary fluid choices.

As we can see the studies provide us with no absolutes. Fluid intake is essential, yet what is in the fluid is also important, as are many client characteristics to consider.

Once we get the fluid into the skin, the real trick is to keep it there and prevent trans epidermal water loss (TEWL) of some 100–150 mls per square metre of skin surface per day (Sparr et al., 2013). That is a story for another day.

This article is an excerpt submitted by Professor Terry Everitt

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