Emulsions, Microemulsions, and Lyotropic Liquid Crystals - Surface and Colloid Chemistry: Principles and Applications - page 194

The skin maintains communication with the underlying part of the body through
pores. A transport of various substances is continuously taking place (such as water,
salts, fats, etc.) through these pores. Thus, an equilibrium exists between these outer
layer and the inside body. However, in some cases, this equilibrium may not be opti-
mum, which leads to skin irritation (red skin, or rashes, or itching). This condition
requires treatment of the skin using cosmetics that are suitable for curing the skin
problem. At present, the personal care industry, which produces cosmetics and their
products, is one of the largest worldwide.
The skin barrier properties and effect of hand hygiene practices are known to be
important in protecting the body. The average adult has a skin area of about 1.75 m 2 .
The superficial part of the skin, the epidermis , has five layers. The stratum corneum ,
the outermost layer, is composed of flattened dead cells (corneocytes or squames)
attached to each other to form a tough, horny layer of keratin mixed with several
lipids, which help maintain the hydration, pliability, and barrier effectiveness of the
skin. This part of skin has been compared to a wall of bricks (corneocytes) and mortar
(lipids) and serves as the primary protective barrier. Approximately 15 layers make
up the stratum corneum, which is completely replaced every 2 weeks; a new layer is
formed almost daily. From healthy skin, approximately 10 7 particles are disseminated
into the air each day, and 10% of these skin squames contain viable bacteria. This is a
source of major dirt inside the house and contributes to many interactions.
Besides covering and protecting the body, the other function of the skin are regu-
lation of the body temperature (ca. 37°C) and also controlling penetration of the
body by sunlight, liquids, solid materials, etc. The human skin is composed of four
layers of different tissue:
The underlying layer or subcutaneous tissue
The dermis or true skin
In the latter region, latter sensory nerves, blood vessels, and sweat glands are located.
Here, a fatty substance called sebum is produced, which coats, lubricates, and keeps
other molecules from passing through the skin. This also has an effect on the water
loss from the body. If for some reason, the outer part of skin is damaged, then special
creams and ointments to repair it are available commercially. These are described in
the following subsection.
9.5.1.1 Fundamentals of Skin creams and recipes
The human skin is a rather complex structure, which protects the body against the
environment. The aim of the different cosmetics is to repair and restore the original
balance of elements in skin structure. Cosmetic preparations would need to consider
any reaction between them and the components of the skin. Skin creams are known
to be composed of a variety of ingredients, which are based on end use (hands,
feet, face, hair, etc.), and some speciality products that are applied to the skin to
repair effects such as dryness. We will now consider some recipes for skin creams.
Since the number of personal care emulsion creams is very large, only a few typi-
cal examples are given here. A variety of emulsion skin care products are found
commercially that claim to exhibit properties for nurturing and protecting the skin.