"Moisturizing" is essential for skincare. Most skincare products claim to provide "hydration" and promote "moisturizing" effects. But what exactly does it mean for the skin to be "hydrated"? As skincare is a daily habit, do we simply judge our skin as "hydrated" based on touch alone? Moisturizing is crucial for maintaining healthy skin. It is a fact that if this is not done properly, the active ingredients in cosmetics will not reach the inner layers of the skin.

Q. First, when in the history of the beauty industry was the state of "hydrated skin" scientifically elucidated?

Hydration has always been a focus, and the term "moisturizing" has been around for a long time. However, it's only recently that more people have been able to properly answer the question, "What exactly is moisturizing?" The mechanism by which skin retains moisture was scientifically understood about 15 years ago, thanks to the discovery of "ceramides."

Q. Was the discovery of ceramides that recent?

The concept of hydration, as in "applying water to the skin," has existed for a very long time. Lotions have also long been considered items for hydrating the skin. However, the discovery of ceramides scientifically proved that these long-held beliefs were incorrect.
Of course, before the discovery of ceramides, various manufacturers were paying attention to hydration and moisturizing. Manufacturers were broadly divided into two groups: those who believed that lipids such as sebum and oils were important for moisturizing, and those who did not. Doctors, in particular, tended to belong to the latter group.
In the research institute where I worked, the prevailing idea was that oily components lead to more hydrated skin. Until the discovery of ceramides, the mainstream belief was that these lipids came from the sebaceous glands. However, it was later found that the lipids produced during the process of keratinocyte differentiation were the most important. These are the intercellular lipids, and ceramides are the prime example. They are substances that firmly bind cells together, hold a moderate amount of water, and allow for the controlled passage of water in and out. It is thanks to these that the skin can comfortably retain moisture. Kanebo was the first to discover ceramides. And Kao's "Sofina" was the first to launch ceramide-related products.

Q. Did the discovery of ceramides significantly change the skincare market?

No, not really. The concept that "skin is hydrated" means that the skin retains moisture, but how that moisture is actually sourced is still not widely recognized. When people hear "moisturizing," they usually think of lotion first, right? Lotions are mostly water, so the traditional skincare advice has been to apply water from the outside and then seal it with a "lid" to prevent it from escaping. Many people still haven't realized that this fundamental concept is wrong.

Q. Rather, the overwhelming majority of people consider that to be the norm.

Certainly, applying lotion wets the skin's surface. But it evaporates quickly. It evaporates and then dries. For example, when your lips are dry, you lick them, right? They feel moist immediately, but don't they become chapped afterward? The same phenomenon is happening with the skin after applying lotion. Of course, lotions contain moisturizing ingredients to prevent immediate chapping, but the skin still dries out over time. That's why oils are necessary to prevent that moisture from escaping.

Q. To provide that oil, emulsions and creams are necessary, aren't they?

No, before even thinking about preventing the escape of externally applied moisture, we must not forget that the skin's moisture originally comes from within the body. Our bodies are 70% water, so it moves from the inside towards the skin's surface and gradually evaporates from the skin. And it is the stratum corneum's ability to retain a certain amount of moisture that makes the skin feel "soft."
For instance, when skin peels off due to chapped corners of the mouth or blisters, that skin becomes dry and flaky, doesn't it? This is because moisture from within the body no longer reaches it. In other words, true moisturizing is achieved only when the mechanism that receives moisture from the body's interior is functioning smoothly in the stratum corneum, and this is what constitutes "hydrated" skin.
The stratum corneum consists of layers of protein called keratin. About 14 of these layers are stacked, and they move upward sequentially through metabolic processes. When they age, they peel off as dead skin cells. The top two or three layers need to be supplemented with lipids, primarily ceramides, to receive moisture from within the body.

Q. So, the conventional idea of "applying moisture to the skin with lotion" is outdated, isn't it?

Regarding "applying lotion to the skin"... while the active ingredients in lotion may penetrate, the water itself doesn't go very deep. "The more you pat, the more moisture enters the skin" is not true. Fundamentally, it is oils, including ceramides, that retain moisture in the skin. Products often advertised with "amino acid formulation" work by helping these components to retain moisture together with oils. Amino acids play a role in dividing labor with lipids like ceramides, resulting in effective moisture retention.
The moisture from lotion softens the skin's surface. As a result, oils can penetrate more easily. The role of lotion's moisture is essentially to soften the skin's surface. However, it only reaches about three layers of keratin sheets on the skin's surface (laughs).

Q. Then, what about "thorough moisturizing with sheet masks"...?

You think that's the norm, don't you? But that's just people in fields other than research, who don't know much about the scientific basis, saying things based on the image that "lotion equals hydration." While it might feel good, from a scientific standpoint, it's a pointless activity (laughs). When you remove a sheet mask and feel moisture on your skin's surface, you get a sense of satisfaction, but to truly achieve hydration, you need to properly replenish with adequate oils.
If it's an emulsion type, you can apply it directly after cleansing. The recent increase in lotions applied after cleansing is likely for this reason. If you want to effectively replenish oils, applying after cleansing is best.

Q. So, we've been mistaking "moisturizing" for a sense of sensory satisfaction?

No, patting lotion isn't entirely a useless step. It's effective as preparation to refine the skin's texture and make it easier to apply oils afterward. But the important thing is that you're not actually adding moisture at that point. The sensation of lotion being absorbed into the skin is not wrong. However, it's only providing water to the surface. The skincare process is complete only when the subsequent step of applying oils is finished, at which point the skin is considered to have "internal moisture."
For a long time, there was a prevailing notion in the market that "oils are bad," and there was also a trend for manufacturers to promote "oil-free" products, so many people have a negative image of oils. Furthermore, Japanese people, who live in a humid climate and enjoy bathing, fundamentally like water, which is why they prefer the feel of lotion. The influence of media information is also significant, and the long-held beliefs that "lotion moisturizes" and "oils are bad for the skin" have hindered the correct approach to moisturizing.

Miyoji Okabe Official Site
The Science of "Beauty"Garden of Beauty Science
http://www.kt.rim.or.jp/~miyoharu/