Our Skin: a protecting barrier
The body's largest organ
Our skin covers approximately 22 sq. feet (2 m2) and weighs about 8 lbs. (3.6 kg), it is the body's largest organ.
The skin is the barrier that protects the body from the surrounding environment: it blocks the damaging ultraviolet radiation from the sun, helps regulate body temperature, insulates us, gives us a waterproof coating and keeps bacteria, toxins and chemicals out of our body. It also prevents our body's water from evaporating away.
It's nerves provides us with sensation (pressure, pain, heat, cold). Its cells synthesize vitamin D and provide a flexible envelope for the body's internal organs.
It is made up of three layers:
The epidermis is the outermost layer. It is the waterproof - protective wrapping of our bodies. It is made up of cells called "keratinocytes" which contain "keratin", a tough proteing (which also makes up our hair and nails).
The outermost layer of the epidermis, which is barely 1 ⁄ 50 inch. thick (0.5 mm) is known as the "Stratum Corneum" (or horny layer) and consist of dead cells which gradually flake off in a process known as "desquamation".
These cells form in the deepest layer of the epidermis and migrate outwards. They are nourished by the oxygen that diffuses from the blood vessels located in the next layer beneath it, the dermis.
This is the second layer, beneath the epidermis. It contains fibers of collage and elastin two proteins which give it flexibility and support.
The capillaries in the dermis regulate the body temperature: increased blood flow allows heat to radiate away from the body through the skin, cooling us, or, during cold weather, restricting the flow to retain body heat.
The hair follicles are rooted in the dermis and the sweat and apocrine glands are located here too.
This is the innermost layer of the skin, it is also known as "hypodermis". It contains a layer of fat, used for both storage and insulation purposes (subcutaneus fat).
Water and the Skin
The body loses water by evaporation, water moves upwards through the skin's layers: the hypodermis, the dermis and it reaches the epidermis. There it works its way through the barrier formed by the Stratum Corneum (SC) and is lost into the atmosphere. This loss is known as "transepidermal water loss or TEWL for short.
When the skin's barrier is breached by chemicals, burns, bites or mechanical damage pathogens (microbes) find their way into the body, and the body begins to lose fluids through the wound.
Fluid loss through burned skin can be quite large. Dr. Charles R. Baxter (1929-2005) devised a formula to work out the "extra" fluid intake so that burn patients remain adequately hydrated.
For instance a person that weighs 165 lbs (75 kg) with burns covering 20% of their body would need to drink an extra 1.58 gallons (6 liters) of fluids per day to keep hydrated.
Epidermis: dryness, water and skin flaking
The water content in healthy Stratum Corneum (SC) - the outermost layer of the skin- is about 10% and it has a role in the normal "desquamation" process by which the external dead skin cells are shed rom the skin. ( 1 )
Natural Moisturizing Factor
This water contains some water binding substances known collectively as Natural Moisturizing Factor (or NMF for short).
NMF contains amino acids (building blocks of proteins), urea, sugars and lactic acid. It is very fond of water (hygroscopic) and absorbs plenty of it, making it a natural humectant. (1)
The SC also contains "hydrolitic enzymes" which are catalysts (substances that activate and speed up chemical reactions) that use water to cleave chemical bonds, dividing large molecules into smaller ones.
The hydrolitic enzymes of the SC clip the protein molecules that retain the dead cells and facilitate the desquamation (flaking) process.
Intercellular Lipid Membranes
There is yet another element in the water-skin balance: the intercellular lipid membranes. These are, as their name implies, ( 3 ) are a matrix of lipids (oily or waxy substances -fats are lipids) that form membranes surround the dead keratin cells of the SC and act as a waterproof barrier against water loss.
Some of the hydrolitic enzymes mentioned further up snip glucosylceramids and phospholipids into fatty molecules that are then used as components for the intracellular lipid membrane. ( 2 )
Causes of Flaky Skin
The outermost dead cells of the SC flake away constantly, these tiny cells are invisible to the naked eye, however under certain circumstances abnormal desquamation can occur, causing "Flaky skin" or what is usually called "Dry" skin.
Dry skin causes the dead cells to clump into visible scales and roughen the surface of the skin, altering its appearance.
There are many mechanisms that can cause Dry of Flaky skin, such as: (1)(2)
- Harsh surfactants in soaps: these can inactivate the hydrolitic enzymes or leach proteins from the skin surface disturbing the natural skin scaling process.
- "Winter dryness" (known as Winter Xerosis -from the Greek word "xeros" = dryness): the dry cold winter air reduces the water content in the SC, provoking extra flaking.
- Aged skin ( 4 ) has slow recovery after wounds and also exhibits a decrese in the production of lipids (fatty substances, particularly cholesterol) which diminishes its barrier properties.
Dry Skin treatment
The usual treatment for dry skin is to use "moisturizers", products which are applied on the skin and add water to it or help the skin to retain water.
Lotions and creams based on propylene glycol, urea, glycerin, some hydroxy acids such as lactic acid are all "Water Holdin" products or humectants.
Others, such as petrolatum form a barrier on the skin that retains water inside the SC (the cream forms an additional barrier that reduces the TEWL (water loss). (1)
But this is only "skin deep"
The moisturizing effect is superficial, at a depth of 1 ⁄ 10 in. (2.5 mm) no water content changes are observed ( 5 ).
Fact or Fiction: Does a low water intake cause Dry Skin?
Hydrate from the inside out?
Some think it is a myth
Another option is to follow what many beauty magazines and websites suggest: increase the amount of water that you drink to improve skin hydration. This is what Akdeniz (2018) ( 6 ) studied, concluding that: "Additional dietary water intake may increase stratum corneum hydration. The underlying biological mechanism for this possible relationship is unknown. Whether this association also exists in aged subjects is unclear. Research is needed to answer the question whether increased fluid intake decreases signs of dry skin."
Akdeniz found that "overall the evidence is weak" but that subjects who drank little water prior to the study had a "Slight increase" in hydration after increasing their water intake.
Wolf (2010) ( 7 ) reached a similar conclusion regarding the recommendation of drinking 8 glasses of water a day for a healthier skin: "We have found no scientific proof for this recommendation; nor is there proof, we must admit, that drinking less water does absolutely no harm..." and hinted that "it is all a myth."
Negoianu and Goldfarb (2008) ( 8 ) agree: " it is not clear what benefit drinking extra water has for skin."
Others believe hydration is good for the skin
Below we list some studies that agree with the notion that hydration (by drinking water) is beneficial for the skin:
Wipke-Tevis (2007) ( 9 ) found that drinking a pint of water (500 ml) increased the capillary blood flow in the skin in healthy adults. They reasoned that being under-hydrated reduces the amount of oxygen in the subcutaneous tissue which in turn hinders wound healing and the risk of infection. However the signifiance or interpretation of how a higher blood flow may impact on skin health are unclear.
Mac-Mary (2006) ( 10 ) studied 80 women and men with an average age of 56 who drank extra mineral water in their daily intake. The study found "Improvements of softness, smoothness and skin-moisturising effect... suggest[ing] that natural mineral water supplementation may be used in order to improve the hydration of skin dryness."
Williams (2007) ( 11 ) studied a group of 86 subjects who drank 2.25 liters of water a day during 4 weeks. They were subdivided into a group drinking tap water and another drinking mineral water. Those who drank the additional mineral water showed a drop in skin density, which is associated to a higher moisture retention. Those drinking tap water on the other hand suffered an increase in skin density (meaning less moisture retention).
Skin thickness increased in the mineral water group and decreased in the tap water group. Skin thickness (thickening of the SC) is believed to be the consequence of water uptake by the cells of the epidermis and water diffusion causes a swelling or physical expansion: thickening, which theoretically should make wrinkles shallower. ( 12 )
However neither group showed improved "Skin morphology" that is regardless of the type of water they drank, their skins' wrinkles, scales or smoothness dit not improve.
Palma (2015) ( 13 ) studied 29 young women (avg. age 24.5), divided into two groups, one (Group 1) that consumed less than 3.2 liters of water a day, the other group (Group 2) which consumed more than 3.2 litres daily. Group 2 then added approx. 2 liters of water to their daily intake for one month.
Over 57% of both groups' water intake was derived from water included in food, juices and soup. The rest came from drinking other beverages, including water.
The study found that:
- No changes in epidermal barrier and TEWL (transepidermal water loss) in other words water lost through the skin remained constant for both groups.
- Superficial and deep hydration improved "dramatically" in both groups.
- Group 1, with an initial lower water intake had the greatest changes.
- Those subjects with dry skin improved significantly.
- "Increasing the dietary water intake would affect the skin the same way as a topical moisturizer"
- It is possible that "more water is available for the normal physiological processes"
The study concluded that: "These results seem to confirm that higher water inputs in one's regular diet might positively impact normal skin physiology, as expressed by its hydratio n and biomechanical behavior, and in particular in those individuals with lower daily water consumptions."
Skin complexion and a Healthy Lifestyle
The studies that confirm a positive effect of additional water intake show a greater impact in those who are under-hydrated. This may suggest that adopting a healthier lifestyle can improve skin complexion.
Castillo (2017) ( 14 ) studied the relationship between healthier dietary habits and skin complexion contemplating other factors apart from water and found that:
- Fruit, vegetable, yogurt consumption were correlated to skin type (improving it)
- Alcohol intake also correlated (having a negative effect)
- Healthy habits plus water intake also improved skin complexion
- No correlation between acne and water intake
Castillo reported that those who drank more water "had healthier habits overall, including exercising and consuming fruits, vegetables, and yogurt, which implies that further assessment is needed to determine which of these factors impact skin appearance and satisfaction."
Castillo's outcome may be the real point behind a good complexion: a healthy lifestyle with a balanced diet and adequate water intake may all contribute towards a better skin.
Cite this article:
A. Whittall. ©2018. Water and skin complexion. Patagonia Wellness, 23 Oct 2018. http://www.patagoniawellness.com/wellness/water-and-skin-complexion.html
Subject: Fact or Fiction: Does a low water intake cause Dry Skin? Adequate hydration is said to improve skin complexion. What does science have to say about fluid intake, dry skin and skin health?
References and Further Reading
(1) Kathi C. Madison et al. (2003). Barrier Function of the Skin: "La Raison d'Être" of the Epidermis. Journal of Investigative Dermatology August 2003Volume 121, Issue 2, Pages 231-241. DOI: https://doi.org/10.1046/j.1523-1747.2003.12359.x
(2) Clive Harding (2005). The importance of intrinsic enzyme activity for stratum corneum health. Journal of the American Academy of Dermatology , Volume 52 , Issue 3 , P41. 100% supported by Unilever Home & Personal Care
(3) Das C, Olmsted PD, (2016). The physics of stratum corneum lipid membranes. Philos Trans A Math Phys Eng Sci. 2016 Jul 28;374(2072). pii: 20150126. doi: 10.1098/rsta.2015.0126
(4) Zettersten EM, Ghadially R, Feingold KR, Crumrine D, Elias PM. (1997). Optimal ratios of topical stratum corneum lipids improve barrier recovery in chronologically aged skin. J Am Acad Dermatol. 1997 Sep;37(3 Pt 1):403-8.
(5) Guzman-Alonso M, Cortazar T., (2016). Water content at different skin depths and the influence of moisturizing formulations. H&PC Today - household and Personal Care today, vol. 11(1) Jan/Feb 2016
(6) M. Akdeniz T. Tomova-Simitchieva G. Dobos U. Blume-Peytavi J. Kottner, (2018). Does dietary fluid intake affect skin hydration in healthy humans? A systematic literature review. Skin Research and Technology. Vol 24:3 Aug 2018, 459-465 https://doi.org/10.1111/srt.12454
(7) Wolf R, Wolf D, Rudikoff D, Parish LC, (2010). Nutrition and water: drinking eight glasses of water a day ensures proper skin hydration-myth or reality?. Clin Dermatol. 2010 Jul-Aug;28(4):380-3. doi: 10.1016/j.clindermatol.2010.03.022
(8) Negoianu D, Goldfarb S, (2008). Just add water. J Am Soc Nephrol. 2008;19:1041-1043
(9) Wipke-Tevis DD, Williams DA, (2007). Effect of oral hydration on skin microcirculation in healthy young and midlife and older adults. Wound Repair Regen 15 : 174 -185, 2007 DOI: 10.1111/j.1524-475X.2007.00202.x
(10) Mac-Mary S et al. (2014). Assessment of effects of an additional dietary natural mineral water uptake on skin hydration in healthy subjects by dynamic barrier function measurements and clinic scoring. Skin Res Technol. 2006 Aug;12(3):199-205. DOI: 10.1111/j.0909-752X.2006.00160.x
(11) S. Williams N. Krueger M. Davids D. Kraus M. Kerscher, (2007). Effect of fluid intake on skin physiology: distinct differences between drinking mineral water and tap water. April 2007 Interntional Journal of Cosmetic Science, Vol 29:2 131-138 https://doi.org/10.1111/j.1467-2494.2007.00366.x
(12) Dabrowska AK et al., (2016). In vivo confirmation of hydration-induced changes in human-skin thickness, roughness and interaction with the environment. Biointerphases. 2016 Sep 15;11(3):031015. doi: 10.1116/1.4962547
(13) Lidia Palma et al., (2015). Dietary water affects human skin hydration and biomechanics. Clin Cosmet Investig Dermatol. 2015; 8: 413-421. 2015 Aug 3. doi: 10.2147/CCID.S86822
(14) Castillo V. (2017). Relationship Between Water Consumption and Overall Skin Complexion Satisfaction in Individuals Ages 18-24. Thesis, Texas Christian University