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Inside-Out/Outside-In Skin Hydration

Contact Author Ginger Hodulik, MS, CNS, DermaMed

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Hydration is an essential part of skin care. Dehydration compromises skin’s immune functioning and causes it to look older and more wrinkled. Skin tissue is constantly being renewed, and depending on the factors produced in the dermis, can be regenerated every 2-3 weeks. Targeted nutrition, both dietary and topical, can dramatically increase the moisture level of the skin. There’s a “nourish from the inside-out and outside-in” story to be told here with skin hydration. Let’s begin by looking at how hydration works in the skin.

The Barrier and Key Players

There are two ways to keep skin moist: by stopping trans-epidermal water loss (TEWL), and by adding moisture from the outside with topical skin care products. The ingredients applied to skin can make a big difference in its hydration status, and just as with dietary nutrition, consider good, clean, topical nutrition options for the best results.

The skin’s barrier, often referred to as the acid mantle, holds in water and lipids and keeps bacteria and environmental pollution out. A crucial part of the acid mantle’s success is its pH. The ideal pH for skin falls around 5.5, which is slightly acidic. Skin with higher pH levels tends to be dry and fragile. Although the purpose of this article is to discuss nutrition for skin hydration, the subject really can’t be covered properly without a brief mention of skin pH, and the importance of not disrupting this pH balance by using harsh topical soaps and treatments.

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Key nutritional players in skin hydration include certain vitamins, essential fats and antioxidants. The inside-out/outside-in story applies here to skin hydration, as with so many other areas of skin care. If these nutrients are taken in through the diet or applied to the skin, results are increased. To build healthy skin, feed the body the right nutrients and protect it from outside damage.

Vitamin C (Ascorbic Acid)

Most estheticians consider vitamin C an essential component in the synthesis of collagen, and as an antioxidant that helps to fight free radical damage in the skin. In addition to these important jobs, this vitamin contributes to skin hydration and elasticity.

While research is not clear on how vitamin C improves skin hydration, a higher intake of dietary vitamin C has been correlated with less dry skin, suggesting it may have effects on TEWL.1

In a study of topical vitamin C, Korean researchers concluded its use in Asian patients undergoing Fraxel skin resurfacing reduced TEWL and helped to restore skin pH levels. This study followed 44 patients undergoing Fraxel, half of which were treated with topical vitamin C and the other half, nothing. Between the two groups, a significant difference in TEWL and skin pH levels was observed, but not in colorimetric status, stratum corneum hydration or skin surface lipids.

The authors concluded, “Topical vitamin C application reduces the injury of the skin’s surface barrier after Fraxel laser and promotes the restoration of skin pH. However, there is a limit with increasing skin lightness or decreasing skin redness.”2

When using vitamin C in skin care routines, it is important to choose the form carefully, as the delivery method can make a big difference in effectiveness. Ascorbic acid, the basic form of vitamin C, oxidizes quickly when exposed to air. Better choices include tetrahexyldecyl ascorbate (the lipid form) or water-soluble sodium ascorbyl phosphate to ensure the vitamin C is delivered to skin without oxidizing.

For delivery of vitamin C from the inside out, it can be obtained in foods such as papaya, bell peppers, broccoli and strawberries.

Vitamin E

Vitamin E is the most potent lipid-soluble antioxidant for skin hydration. It is an essential part of skin cell membranes and has a role in cell signaling and cell nutrient transport. Therefore, it appears to enhance the penetration and resorption of skin lipids, creating an effective regulatory mechanism for restoring and maintaining the barrier function.3 Topically applied vitamin E is a moisturizer that helps keep the skin healthy and soft.

Vitamin E exists in eight chemical forms. There are two main categories of this complex vitamin— tocopherols and tocotrienols—and each contains four types of molecules: alpha, beta, gamma and delta.4 Tocotrienols are 40-60 times more effective at quenching free radicals than tocopherols.5

Vitamin E has a special relationship with two other antioxidants—vitamin C and alpha lipoic acid. Both vitamin C and alpha lipoic acid are capable of removing the extra electron from a used vitamin E molecule, essentially reactivating it. This capacity to recycle and restore its power makes vitamin E a prominent factor in the skin’s first line of defense against free radicals.6

Thus, vitamin E plays an important role in maintaining the barrier function of skin and appears to enhance the penetration and resorption of skin lipids, making it an invaluable nutrient for locking moisture into the skin and preventing dehydration.7 Good food sources for obtaining vitamin E are nuts, seeds and vegetable oils.

B Vitamins

The B vitamins are a complex and busy group but offer a wealth of benefits for skin, internally and externally.

B3, Niacin. One important B vitamin is B3, also referred to as niacin or nicotinic acid. This B vitamin has three critical roles in the body: converting glucose to energy, aiding in the production of fatty acids and cholesterol, and facilitating DNA repair and stress responses.

As a player on the topical nutrition team for skin hydration, niacinamide (its skin care form) increases the production of ceramides and fatty acids, two key components of skin’s outer protective barrier. With a strong acid mantle, the skin is better able to keep moisture in and irritants out.

Dietary sources of vitamin B3 or niacin include tuna, chicken, turkey and peanuts.

B5 Pantothenic Acid. Vitamin B5 is a component of coenzyme A (CoA), an essential coenzyme required for chemical reactions that generate energy from food (fat, carbohydrates and proteins). It also is involved in the synthesis of essential fats, cholesterol and steroid hormones such as estrogen and testosterone.

On the topical side, B5 contributes to skin hydration via its role in the maintenance of skin barrier function. When applied to skin, B5 converts to pantothenic acid, which works as a humectant by infusing water in the cells, retaining moisture deep within the skin tissues.8

In the diet, good sources of vitamin B5 include avocado, lentils, shiitake and crimini mushrooms.

Vitamin A (Retinol)

Vitamin A is fat-soluble and comes in various forms: retinol, retinal and the various retinol esters. Among other important functions, vitamin A supports cell growth and differentiation, which is how it may contribute to hydration in the skin.

In topical form, vitamin A improves hydration in and around skin cells in a number of indirect ways, mostly by supporting healthy cell membrane functioning and encouraging skin cell turnover. In doing so, nutrient transport, waste removal and a reduction in TEWL result.9 Many forms of topical vitamin A are available for skin care formulations. The main goal is to balance delivering an effective amount of vitamin A to the skin while managing the side effects that often accompany vitamin A application.

Retinoic acid is an effective, bioavailable form of vitamin A, but it causes the most side effects. Retinols are also effective but must undergo a transformation to retinoic acid when applied to the skin. Many skin care ingredient manufacturers have developed technologies such as encapsulation to lessen the side effects while improving delivery. The least harsh, yet less effective forms are retinyl acetate, retinyl linoleate, retinyl palmitate and retinyl proprionate.

It is critical for clients to get adequate vitamin A each day through dietary sources and by applying a topical dose to skin as part of their regular skin care routine. Dietary vitamin A comes from sweet potatoes, carrots, dark green leafy vegetables, dairy, fish and meat. Liver also is an excellent source of vitamin A. While foods rich in beta carotene supply vitamin A, only a small percentage is converted.

Fatty Acids

Certain dietary fats, referred to as essential fatty acids, are essential because the body cannot manufacture them, so they must be included in a diet to avoid deficiency. These fats fall into two categories: omega 6 (O6) and omega 3 (O3).

The standard American diet (SAD) typically consists of too much O6 and too little O3. The recommended intake of O6 to O3 is a 2:1 ratio, yet the SAD diet sees closer to a 12:1 ratio. This imbalance leads to an inflammatory state due to the pro-inflammatory hormones created by an overabundance of O6 fats.

This is a case where the “inside-outside” story is powerful, as chronic inflammation triggers a vast number of inflammatory skin conditions such as psoriasis, rosacea, eczema and acne. Although inflammation is not the same as dehydration, it contributes to a higher need for water in our cells and decreased cell membrane function. Conversely, when the body is deficient in both types of dietary fatty acids, skin cell integrity suffers and barrier function is reduced.

A dietary deficiency in these fatty acids results in a characteristic scaly skin disorder, increased epidermal turnover rate, weak cutaneous capillaries that rupture easily, decreased wound healing, and increased TEWL leading to dry skin.10 Topically, fatty acids are key players in skin hydration, but the best delivery vehicle is from the diet.


Omega 6. O6 fatty acids provide hydration in the skin by maintaining epidermal homeostasis, meaning they balance the flow of fatty acids in and out of cell membranes.11 The most noteworthy O6 fatty acid used in topical formulations is gamma linolenic acid (GLA) from borage and evening primrose oil. GLA is one of the most effective agents for the treatment of skin disorders and for the maintenance of healthy skin. Studies show it is beneficial for the treatment of skin conditions including dry skin, eczema, inflammation, wounds and dermatitis.12 Dietary O6 fats come from vegetable oils such as palm, soybean and canola.

Omega 3. O3 fatty acids support the skin cell membranes of the epidermis, allowing for nutrient transport in and out of the cell, as well as the removal of waste. An intact skin cell membrane is better able to hold onto water, thereby increasing hydration in the skin. Although a good source of O3, fish oil is not a desirable ingredient in skin care due to its fishy smell and the heaviness of the oil. Preferred sources for topical skin care include algae and other marine plant sources. Dietary O3 fats are found in fatty fish and fish oil, flaxseed and walnuts (in much lower levels).

Lutein and Zeaxanthin

Many antioxidants and phytochemicals benefit the skin. Research has found that the daily consumption of 10 mg of lutein and 2 mg of zeaxanthin increases skin hydration, skin elasticity and superficial lipids. However, when dietary intake was combined with topical application, the hydration status improved 20%.13 Lutein and zeaxanthin are nutrients found in dark green, leafy vegetables such as kale and spinach.

An Important Combination

Combining dietary and topical nutrition for skin health is especially important for skin hydration. This article explored some of the most clinically significant players, but there are many other beneficial compounds. The key message remains the same: consume a diet rich in colorful fruits and vegetables every day and take care when choosing sources of nutrition for skin. Clean diet and skin care on the inside = healthy, glowing skin on the outside.


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  12. P Palombo et al, Beneficial long-term effects of combined oral/topical antioxidant treatment with the carotenoids lutein and zeaxanthin on human skin: a double-blind, placebo-controlled study, Skin Pharmacol Physiol 20(4) 199-210 (2007)
Ginger Hodulik

Ginger Hodulik, MS, is a Certified Nutrition Specialist (CNS) with both bachelor’s and master’s degrees in nutrition. She has worked in clinical practice and wellness program development and implemen­tation. Currently, she serves as co-owner and VP of R&D for DermaMed Solutions.

Ginger Hodulik, MS, is a Certified Nutrition Specialist (CNS) with both bachelor’s and master’s degrees in nutrition. She has worked in clinical practice and wellness program development and implemen­tation. Currently, she serves as co-owner and VP of R&D for DermaMed Solutions.