Summarizing winter in a mathematical formula,
Winter (Low temperature, Dry weather) = Winter skin (Dehydrated skin)
In winter, dehydrated skin is more common than in summer. The shift in humidity and temperature dehydrates and disrupts the skin barrier, causing it to seem dull, cracked, flaky, and itchy, as well as causing increased sensitivity and the appearance of fine lines and wrinkles. Dehydrated and damaged skin needs moisture replenishment. The most effective way to replenish moisture in the skin and prevent water loss is to use a moisturizer.
Let us understand the science underlying shrivelled skin and the significance of moisturizers,
1. The interplay of winter with the dry skin
Our skin contains a certain quantity of water on its surface. The exterior low temperature and the interior warmth (indoor heating) capture the skin's natural moisture. When the temperature is cold, the humidity is low, thus resulting in a drop in the moisture content of the air [1]. This dry air dehydrates the skin by drawing moisture from the surface of the skin. This leads to dehydration that causes the skin to become dry, red, itchy, rough, flaky, cracked, and uncomfortable.
2. Skin's ability to reduce water loss
The outermost layer of the skin is biologically dead but biochemically very active. It is made up of skin cells known as corneocytes that contain the skin’s natural moisturizing factor (NMF). The skin’s NMF plays an important role in reducing the loss of water from the surface of the skin (trans-epidermal water loss, TEWL) and keeping it hydrated [4].
Figure 1. Corneocytes containing the natural moisturizing factor [3]
3. Where does the skin’s natural moisturizing factor (NMF) come from?
The NMF of the skin is produced in the corneocytes by the breakdown of the protein called filaggrin. It is composed of free amino acids, and various derivatives of the amino acids that are the by-products produced by the breakdown of the filaggrin. [4]
4. Role of NMF
Figure 2. Production of NMF
The components of the NMF are a) urocanic acid that acts as a natural absorber of ultraviolet (UV) light, b) urea that acts as a strong moisturizing agent and it also prevents scaling of the skin and is used to effectively treat dry skin, c) lactic acid or lactate that belongs to a group of compounds called alpha hydroxy acids (AHAs) that act as chemical exfoliants that remove dead skin cells from the outermost layer of the epidermis, to make way for new cell generation, d) ceramides that help to soothe skin irritation and provide additional barriers to prevent loss of moisture and dry skin e) hyaluronic acid that is a powerful humectant capable of binding more than 1000 times its weight in water.[4]
5. Does the environment influence the body's natural moisturizing factor (NMF)?
Yes, it does! The skin’s NMF is a reflection of the external environment. Based on the weather conditions, the body can control how much NMF needs to be produced. The skin starts producing more NMF in low-humidity environments, whereas it produces less NMF in high-humidity environments [1]. However, when the skin lacks adequate water, the proteolysis of the filaggrin cannot take place because the enzymes are unable to work in a dehydrated state. [4] As a result, the skin's NMF cannot be produced.
Furthermore, extensive bathing (surfactant components) or UV light exposure reduces NMF production. Similarly, NMF production is also affected by age. As a result, one of the most frequent skin aging problems is dull and dry skin.
6. Importance of Moisturizers
As NMF is found within skin cells, topical products cannot encourage the skin to produce additional NMF.[6] To keep the skin hydrated throughout the winter, synthetic moisturizers must be used. These moisturizers function similarly to the skin's natural moisturizing factor. They contain substances such as urea, lactate, amino acids, and pyrrolidone carboxylic acid (PCA[LF1] ), which are components of natural moisturizing factors (NMF).[2] Moisturizers can be categorized into three classes: (1) emollients, which soften and smoothens the skin; (2) occlusives, which provide a barrier that sits on the surface of the skin and prevents transepidermal water loss (TEWL); and (3) humectants, which bind and hold water in the stratum corneum.[5]
The best approach is to use a barrier repair moisturizer. This type of moisturizer mimics your skin’s natural 1:1:1 ratio of cholesterol, fatty acids, and ceramides to help it hold moisture and keep irritants sealed out.[6]
Thus, winter seems to be a welcoming season for Moisturizers!
References:
1. Goad N, Gawkrodger DJ. Ambient humidity and the skin: the impact of air humidity in healthy and diseased states. J Eur Acad Dermatol Venereol. 2016 Aug;30(8):1285-94. doi: 10.1111/jdv.13707. Epub 2016 Jun 15. PMID: 27306376.
2. Chauhan, Lalita & Gupta, Shalini.Creams: A Review on Classification, Preparation Methods, Evaluation and its Applications. Journal of Drug Delivery and Therapeutics (2020)10. 281-289. 10.22270/jddt.v10i5-s.4430.
3. Rosso, James Del et al. Understanding the Epidermal Barrier in Healthy and Compromised Skin: Clinically Relevant Information for the Dermatology Practitioner: Proceedings of an Expert Panel Roundtable Meeting.The Journal of clinical and aesthetic dermatology vol. 9,4 Suppl 1 (2016): S2-S8.
4. Fowler J (2012, July). Understanding the Role of Natural Moisturizing Factor in Skin Hydration - Practical Dermatology. Accessed on 10th January 2023.
5. Alivio A. (2022, December 13). Kiss dry and dehydrated skin goodbye. Emotion: An Erasmus Mundus student Project. Accessed on 10th January 2023.
6. Baumann L. (2019, December 9). What Is Natural Moisturizing Factor (NMF)? Leslie Baumann M.D Cosmetic Dermatologist. Accessed on 15th January.
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