The human body is approximately 60% water. Water has vital functions in our everyday living as it aids in body temperature regulation, metabolism of carbohydrates and proteins, cellular functions, nutrient transport, flushing of wastes, and more.[1] Water is also present in our skin, about 64%,[2] and it is absolutely essential for the proper functioning of the skin.
The skin acts as a barrier, preventing dryness, infection, mechanical stress, and chemical irritation in the underlying tissues. When this function is impaired, there is an increase in trans-epidermal water loss that leads to various kinds of skin problems.[5]
Dry versus dehydrated skin
The terms "dry" and "dehydrated" are sometimes used interchangeably, however, they are not synonymous. Dry skin is characterized by a chronic lack of sebum, or oil, on the skin. It is usually accompanied by unpleasant symptoms such as itching, cracking, or flaking. Genetics plays a major role, but it can also be aggravated by internal and external factors such as extreme temperatures, using strong skincare treatments that deplete the skin of its natural oils, medical disorders, lifestyle, hormones, and the natural aging process.[3]
Dehydrated skin, on the other hand, refers to a lack of water in the skin which could be caused by a weakened skin barrier, a lack of water in the diet, or harsh weather (cold, dry climates, in particular, are associated with dehydration). Dehydrated and dry skin have many similar symptoms, such as dullness, roughness, and elasticity loss. However, while dry skin is a distinct skin type, dehydrated skin can affect anyone, including those who have naturally oily skin.
How moisturizers prevent dry and dehydrated skin
The skin is made up of layers (see Figure 1) and water flows upward from deeper epidermal layers to hydrate stratum corneum cells before evaporating. The amount of water in the epidermis is critical for preventing skin dryness and maintaining flexibility. The stratum corneum is an active membrane that has been described as a brick-and-mortar model, in which the loss of intercellular lipids that form bilayers (ceramides, cholesterol, and fatty acids) causes damage to the water barrier, resulting in dry skin.[5]
Figure 1. Cross-section through the skin[7]
Moisturizers are important components of basic skincare that help protect the skin by stimulating its natural barrier function and keeping up with its constant demand for moisture.[8] Table 1 shows the different types of moisturizing ingredients and their mechanism of action.
Table 1. Types of Moisturizing Ingredients [5,6,9]
Type | Description | Mechanism of Action | Ingredients |
Emollients | Saturated and unsaturated hydrocarbons with variable length which improves skin barrier function, membrane fluidity and cell signaling, resulting in overall improvement of skin texture and appearance. Often combined with emulsifier | Emollients fill up rough patches and make skin feel smooth, but they have little effect on the amount of water in the skin.  | Fatty alcohols, Fatty acids, Ceramides, Jojoba oil, Dimethicone, Cholesterol, Squalene |
Humectants | Low molecular substances in majority, with capability to attract water into stratum corneum. Frequently used with other compounds which may retain the water content | Water is sponged up by humectants, which pull it up from the dermis and, to a lesser extent, from the air in humid conditions.  | Butylene glycol, Glycerin, Hyaluronan, Panthenol, Sodium PCA Urea, Sorbitol, Propylene glycol |
Occlusives | Consist of oils and waxes, forming an inactive layer on the skin surface to physically block water evaporation from the skin (trans-epidermal water loss) | Water is held in by occlusives after it has been provided by a moisturizer or a soak in water.  | Petroleum jelly, Mineral oil, Silicones |
A typical commercially available moisturizer contains a combination of all three types of ingredients. The addition of occlusives and humectants improves the skin's water-holding capacity while the addition of certain emollients to moisturizers may increase the esthetic quality and stability of the active components.[5] Moreover, most moisturizers directly provide water to the skin (water-based). They also cover small skin fissures, provide a soothing protective film, and protect skin from friction.
Moisturizers are essential in keeping our skin from dryness and dehydration, which helps in maintaining overall skin health. So, the next time you go to your favorite drugstore, make sure to grab a moisturizer and kiss goodbye to dry and dehydrated skin.
References:
[1] Water Science School 2019, USGS, accessed 27 May 2022 <https://www.usgs.gov/special-topics/water-science-school/science/water-you-water-and-human-body#:~:text=In%20adult%20men%2C%20about%2060,their%20bodies%20made%20of%20water>
[2] James Roland 2019, Healthline, accessed 27 May 2022 <https://www.healthline.com/health/body-water-percentage#body-water-storage>
[3] Mayo Clinic 2022, accessed 27 May 2022 <https://www.mayoclinic.org/diseases-conditions/dry-skin/symptoms-causes/syc-20353885#:~:text=Living%20in%20cold%2C%20windy%20conditions,oils%20from%20your%20skin%20too>
[4] Krissy Brady 2021, Prevention, accessed 27 May 2022 <https://www.prevention.com/beauty/skin-care/a36292880/how-to-hydrate-skin/>
[5] Purnamawati, S., Indrastuti, N., Danarti, R., & Saefudin, T. (2017). The Role of Moisturizers in Addressing Various Kinds of Dermatitis: A Review. Clinical medicine & research, 15(3-4), 75–87. https://doi.org/10.3121/cmr.2017.1363
[6] Harvard Health Publishing 2019, accessed 27 May 2022 <https://www.health.harvard.edu/staying-healthy/moisturizers-do-they-work>
[7] Nursing Times 2019, accessed 27 May 2022 <https://www.nursingtimes.net/clinical-archive/dermatology/skin-1-the-structure-and-functions-of-the-skin-25-11-2019/>
[8] Verdier-Sévrain, S., & Bonté, F. (2007). Skin hydration: a review on its molecular mechanisms. Journal of cosmetic dermatology, 6(2), 75–82. https://doi.org/10.1111/j.1473-2165.2007.00300.x
[9] Bao Ngoc Nguyen 2020, EMOTION, accessed 25 May 2022 <https://www.emotion-master-studentproject.eu/post/cosmetic-ingredients-101-moisturizer-analysis-humectant-infographic>
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