Evidence for the existence of a body‐brain connection for skin moisturization

Abstract

Maintenance of the right water levels in the skin is of crucial importance to maintain healthy, young‐looking skin. Moisturizing products have therefore aimed to influence the constitutive levels of natural moisturizer factor (NMF) and/or the formation of the skin lipid barrier. In humans, keratinocyte differentiation is influenced by sex hormones, in particular positively by estrogen and negatively by testosterone. It has been noted that postmenopausal women experience a decline in estrogen levels and a concomitant drop in skin moisturization. In our previous near‐infrared reflectance (NIR) spectroscopy work on human skin, we noted that skin moisturization was influenced by gender, age, psychological stress and lifestyle habits such as alcohol consumption and smoking. Many of these also affect the level of sex hormones. We therefore re‐evaluated NIR spectra from which we had already assessed the levels of skin moisturization in human volunteers to determine their levels of estrogen and testosterone non‐invasively. We subsequently built mathematical models to link skin moisture content to the levels of these sex hormones. In this way, we were able to establish the importance of sex hormones in skin moisturization. In men, skin moisturization levels are linked to their estrogen levels, whereas in females, skin moisturization levels are linked to both estrogen and testosterone concentrations. From the medical literature, it is known that smoking is associated with increased testosterone and reduced estrogen levels, which suggests that people that smoke are characterized by less hydrated skin as well as by increased testosterone levels. On the other hand, pregnant females that have significantly elevated estrogen to progesterone ratios, i.e. their increase in estrogen level exceeds their increase in testosterone levels, also often remark that their skin is well hydrated, confirming the link between sex hormone levels and skin moisturization. For them, we found a good correlation coefficient for skin moisturization levels and their estrogen to testosterone ratio.This work does not, however, answer question of a cause‐and‐effect relationship between the two. Increased levels of estrogen can either directly increase skin moisture levels or do so via a positive effect on skin barrier formation. It does, however, reveal once again the existence of a connection between our body (the skin) and our brain. Synthesis of sex hormones is regulated via the pituitary gland in our brain and it can therefore be argued that skin moisturization is directly or indirectly regulated via our brain. As many other factors like smoking and alcohol consumption actually influence estrogen levels in our blood, the influence of our brain on maintaining a skin moisture homeostasis may actually be much more pronounced than hitherto assumed.