Introduction

“Moisturization” is a term that has different meaning based on its intended purpose and how it is being applied. In order to understand this term, one needs to understand what is really happening when a moisturizer is applied to skin (hair and/or underarm). Most people use moisturizers to hydrate dry skin, repair and prevent rough cracked skin, restore natural feeling skin that is plush and soft/silky/smooth, or alleviate a skin condition such as eczema, contact dermatitis, or rosacea. Bottomline, most people just want their skin to feel and look nice without any discomforts.

Interestingly, humans have been using some sort of topical moisturizer for the past 10,000 years. Ancient Sumerians from the current day Iraq region used natural salves from minerals, animals, and pulverized plants, to Latin Americas using palm oil and avocado oil, to Native American tribes using animal fat and tree oils to keep skin soft. Most of these concoctions were crudely prepared and it took a Greek Physician, Aelius Galenus (Galen) in the early 200s AC to create a cold cream moisturizer using rose oil and made as a beeswax and water emulsion; improved manufacturing processes in the 1800s that are still used today but replacing rose oil with other skin conditioning ingredients (such as petroleum jelly, lanolin, and fatty acid esters). Today there are thousands of body creams and moisturizers available with more than 80% of women in the United States claiming to use body or hand lotion on a regular basis.

The scope of this chapter will be focused on the connection with skin, and what is really going on topically when skin conditioners/moisturizers are applied. To do this, we will start off with a brief explanation of skin physiology – though Part 1, Section 1, Chapter 1 will explain skin (hair) physiology in more depth. We will then go into characterization of skin conditioners, defining them, and then transition into how you test each type of skin conditioner – you will find more thorough explanations of testing in Part 1, Section 1, Chapter 5.

Basic physiological mechanism of skin moisturization

It is important in personal care cosmetic applications, that products applied topically do not create a physiological action, otherwise, they will be considered drug‐like, or at the very least, more than just a cosmetic. So, we will direct this chapter to what is taking place in the stratum corneum.

The epidermis is the very topmost layers and represents a mere 15–25 μm thick (0.05–1.5 mm). It is built up from layers below that migrate to the surface overtime and begin to die. This is the key barrier to protect what is below it from being contaminated and negatively affected by the exposed environment. It is made up primarily of keratinocytes. The epidermis is conventionally divided up into a basal layer of keratinocytes containing, in particular, skin stem cells and constituting the germinative layer of the epidermis, a “spiny” layer constituted of several layers of polyhedral cells placed on the basal layer, a “granular” layer, and finally, a set of upper layers, called horny layer or stratum corneum, constituting keratinocytes at the terminal stage of their differentiation, called corneocytes.

1. More specifically, the epidermis is a structure of which the homeostasis results from the implementation of a finely regulated collection of intracellular and extracellular signals acting during all the steps of cell proliferation, migration, and differentiation, and also the steps of synthesis of the various extracellular matrix components. For this chapter on the four key elements of moisturization, we will focus mainly on the outer layer of the epidermis/stratum:
   
   
   
   1. The stratum is the outermost part of the skin and performs the function of a barrier between the organism and the environment;
      
   2. Epidermal differentiation follows a process of maturation in which keratinocytes of the basal layer differentiate and migrate so as to result in the formation of corneocytes, which are completely keratinized dead cells. This differentiation, when skin conditions are healthy, results in a perfectly coordinated phenomenon, which will result in the thickness of the epidermis being kept constant and thus ensure the homeostasis of the epidermis;
      
   3. The stratum is most important in modulation of skin’s moisture content – when this layer is damaged or compromised, the result is increased trans‐epidermal water loss (TEWL) that is noticed by the consumer as dry skin, cracking skin, irritated skin, less flexible skin.
   
   
2. The next layer is the dermis and it is made up of loosely bundled structural protein collagen and elastin fiber. Its thickness varies from 0.3 to 3.0 mm dependent on location on the body; and is divided into two layers, papillary and reticular layers.
   
3. The last layer is classified as subcutaneous tissue or hypodermis, and is the last layer of protection from the environment, acting as an insulator and provides a fair amount of skin resiliency.

What is healthy skin

The skin is in a naturally healthy state when the moisture in the skin’s topical layers is optimally modulated. That is to say, the skin’s barrier provides equilibrated trans‐epidermal water maintenance. But we live in the real world and many things can affect the healthy balance of skin; where the external environment and aging can have damaging impact on proper moist modulation. If we put nutrition to the side, we can look at other external environmental issues that affect the health of skin. The external issues that can affect the health of skin are air pollutants, sun, surfactant washing, and mechanical rubbing. So we need a way to prevent or minimize these stimuli from affecting the skin.

All of these external and internal stimuli effect of the integrity of skin’s barrier, causing the skin’s barrier to have to work harder to maintain the correct modulation of skin moisture. The more damaged or compromised the skin is, the hard it has to work.

As mentioned before, but the author feel this point is important enough to repeat, healthy skin has the proper balance of moisture. An imbalance can cause many problems, some are rather rapid and others deal with changes over time.

Related posts:

36: Botanicals 15: Hand Cleansers and Sanitizers 41: Topical Vitamins 59: Eczema Regimens 22: Antiperspirants and Deodorants 29: Colored Nail Cosmetics and Hardeners

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