Myth: Oily Skin Doesn't Need Moisturizing.

A common misconception is that oily skin does not need to be moisturized. The fact that it produces excess sebum (reactive hyperseborrhea) would prompt one not to add to it with the application of a moisturizing product, thinking that it might be counterintuitive. Even if it seems surprising, oily skin can also suffer from dehydration with consequences on the skin's look and feel: tightness, irritation, redness...

Our skin naturally loses water every day through sweat and evaporation (skin perspiration). In physiological conditions, this loss is about 5 grams per square meter per hour. These water movements contribute to the proper physiological functioning of the stratum corneum by providing a continuous source of hydration. This rate of hydration influences the apparent macroscopic parameters (elasticity, softness...) but also the molecular parameters, the activity of the enzymes and the cellular signaling within the epidermis.

Indeed, although a large majority of water is stored in the form of a semi-fluid gel thanks to its attachment to hydrophilic macromolecules (collagen, hyaluronic acid) in the dermis, part of it remains mobilizable and diffuses passively towards the epidermis. The skin is also constantly subjected to external aggressions: pollution, allergens, microbes, UV rays, lifestyle (smoking, alcohol, etc.), excessive cleaning/scrubbing, hair removal, etc...

Thus, to maintain an optimal water gradient in the skin, it is essential to moisturize it even if it is oily. Applying a moisturizer will help the skin to limit this insensible loss of water (PIE), to act as a barrier against external aggressions and at the same time to rebalance the sebum level. This is an important step to take, especially when the skin is subject to the effects of climatic variations (wind, cold, humidity, heat, etc.), and when the hydrolipidic film may be weakened and the skin can no longer retain water. In addition, when the epidermal barrier is damaged and the skin is attacked by external elements, the sebaceous glands are stimulated and produce more sebum to protect it.

The objective of this gesture is not to hydrate strictly speaking, but rather to prevent the dehydration of the skin by protecting the hydrolipidic film. In fact, the term "moisturize" commonly used in cosmetics is not entirely appropriate. On the contrary, providing oily skin with a cream will allow the "fatty" elements to reinforce or reconstitute the lipid barrier. In addition, protecting and soothing oily skin will gradually regulate its overproduction of sebum. Therefore, these moisturizing formulations consist of maintaining an optimal level of water within the epidermis in order to preserve its functionality, while restoring the barrier role of the stratum corneum and the hydrolipidic film.

Skin hydration depends on the integrity of the cutaneous barrier, composed of the hydrolipidic film and the stratum corneum. The use of a moisturizing product is therefore recommended, even for oily skin. For this type of skin, it is particularly advisable to opt for a gentle care product in the form of an oil-in-water emulsion, which is considered light, smooth and moisturizing upon application, and whose composition combines matifying effectiveness with active ingredients such as zinc, copper, bamboo extract, green clay, activated charcoal, etc.) and moisturizing of the epidermis.

Furthermore, it is important that this product is non-comedogenic, i.e. it will protect the skin without clogging the pores, and sebo-regulating, i.e. in addition to preserving the hydration of the epidermis, it should also purify and balance sebum production. Regarding the hydration strategy, the care product must contain substances such as :

• Humectants/hygroscopic agents: These active ingredients will bind to the stratum corneum and allow transepidermal water to be trapped within the cells of the stratum corneum. We can cite glycerin, aloe vera, panthenol, low molecular weight hyaluronic acid, sodium PCA, hydrolyzed collagen, urea, sodium hyaluronate, fructose... ;

• Hydrophilic film-forming agents: These compounds are capable of retaining numerous water molecules in their membrane, thus forming a hydrogel on the surface to slow down water loss. We can mention high molecular weight hyaluronic acid (up to 1,000 times its weight in water), polyglutamic acid (up to 5,000 times its weight in water), high molecular weight collagen... ;

• Emollients: These are lipids that mimic those that constitute the intercellular bonding of the epidermis. They are integrated into the lipidic matrix in order to fill the micro-cracks between the cells of the superficial layers of the epidermis, and thus have an action known as internal occlusion. They are essentially vegetable oils rich in polyunsaturated fatty acids and free lipids (fatty acids, fatty alcohols, fatty acid esters, sphingolipids, ceramides, squalane, stearyl alcohol...).

If the first objective is to bring a hydrating and matifying care, this last one must also contain anti-inflammatory assets (ex: niacinamide, aloe vera, etc...) and antibacterial (ex: azelaic acid, bakuchiol, salicylic acid, essential oil of tea tree, etc...). Indeed, oily skin tends to provide bacteria with the ideal conditions for rapid and lasting proliferation.