So how to judge if skin is moisturized? And what ingredients are adopted to help dry skin?
Usually, there are three typical ways scientists adopt to judge skin moisturizing. They are sensory, quantitative evaluation and instrument measurement. If a product can meet good moisturizing criteria on these 3 areas, we can say it’s a good efficacy product; and as R&D people, they can release to production and commercial. I won’t talk in detailed of these methods. But I’ll separately discuss in other articles how to combine the typical 3 studies to make superior consumer preferred product claims as R&D people.
The normal water content level in stratum Corneum is around 10-15%. At this level, skin stays comfortable, good appearance, touches supple. Below 10%, skin will feel and looks dry, and when you touch, it will feel rough, not smooth enough. If it goes to much lower level will bring crankiness on skin. When I worked on emerging market project, given those people are usually working under severe dry/cold condition, we deliberately designed a product that help immediately and recover from skin crack. I also joined another winning product design. The target consumer would rather believe their own experience on good moisturizing vs. our advertisement or even data. So we spend huge effort in identify their sensory profile and tried to transfer into technical design items. Both were winning product that I still remember it clearly.
When formulator is making formula, the best way to protect water from evaporation and best way to maintain water is to offer a similar-to-skin ingredients that best matches skin activity in stratum corneum. In order to protect water from evaporate, it needs to firm an oil layer on skin. So, you could always notice the humectant ingredients in the formula.
The second method is to maintain water in skin. The most typical ones are NMF (Natural Moisturizing Factor). If the skin barrier function is destroyed, or when the NMF level in skin decreases, skin will became dry visibly and sensibly. The key elements in NMF contain amino acid, lactate, urea, ceramide, etc. So a good combination of NMF in formula supports the water to be secured to skin.