461
is extremely complex. Emulsions consist of stable mixtures of small
droplets of one liquid dispersed and suspended in a second liquid,
with the two liquids not normally being mixable. Common cold
creams are often emulsions. Many emulsions are based on lipids or
lipophilic compounds (materials that do not dissolve in water but
can dissolve in alcohol) and water, or on lipophilic compounds
that have an affinity for oil or can combine with it and hydrophilic
compounds that combine with water. Either “oil in water” or “water
in oil” types are possible. Aerosols are dispersions of small solid or
liquid particles suspended in a gas. Many perfumes are aerosols, as
are some hair products and even colorization mists. (There are also
many pharmaceutical aerosols in use, such as local anesthetics or
antifugal or anti-inflammatory aerosols). Aerosols can contain quite
tiny particles at the nanoscale. Once applied, carriers can undergo
many changes due to exposures to other substances, mechanical
factors (wear, stress), evaporation of some volatiles, and other
factors.
The current efficacy of these products stems from a considerable
body of research into both the physical and biological characteristics of skin structures and into processes such as skin aging as well.
Skin is known to serve barrier, thermal control, and a host of other
functions for maintaining life, such as the creation of vitamins.
Skin is composed of several primary layers: the epidermis, the
dermis, and a subcutaneous layer. The epidermis is composed of
five strata. The outer layer, the stratum corneum, provides a protective barrier of dead cells that are tough and not soluble and that
are continuously replaced by new cells growing from below. It does
not contain blood vessels. The thicker dermis holds nerves, blood
vessels, and sweat glands as well as providing other functions. The
subcutaneous layer is essentially fatty. This complex layering has
many physical and chemical properties that change and evolve with
time (also see Figure 11.2).
Skin necessarily exhibits interesting mechanical properties in
its barrier- and shape-maintaining functions that derive from an
elastic collagen (long fibrous proteins) network. With time these
properties can change, usually leading to relaxations in stiffness
and tensions that in turn are manifest as “aging wrinkles” or flaccidness. With respect to light and optical phenomena, many kinds
of absorption properties exist at different layers that can again
vary with time. Chemical actions are equally remarkable. Needed
vitamin D, for example, is produced photochemically in the skin,
largely in the stratum basale and stratum spinosum layers of the
epidermis.
Nanoproduct Forms
is extremely complex. Emulsions consist of stable mixtures of small
droplets of one liquid dispersed and suspended in a second liquid,
with the two liquids not normally being mixable. Common cold
creams are often emulsions. Many emulsions are based on lipids or
lipophilic compounds (materials that do not dissolve in water but
can dissolve in alcohol) and water, or on lipophilic compounds
that have an affinity for oil or can combine with it and hydrophilic
compounds that combine with water. Either “oil in water” or “water
in oil” types are possible. Aerosols are dispersions of small solid or
liquid particles suspended in a gas. Many perfumes are aerosols, as
are some hair products and even colorization mists. (There are also
many pharmaceutical aerosols in use, such as local anesthetics or
antifugal or anti-inflammatory aerosols). Aerosols can contain quite
tiny particles at the nanoscale. Once applied, carriers can undergo
many changes due to exposures to other substances, mechanical
factors (wear, stress), evaporation of some volatiles, and other
factors.
The current efficacy of these products stems from a considerable
body of research into both the physical and biological characteristics of skin structures and into processes such as skin aging as well.
Skin is known to serve barrier, thermal control, and a host of other
functions for maintaining life, such as the creation of vitamins.
Skin is composed of several primary layers: the epidermis, the
dermis, and a subcutaneous layer. The epidermis is composed of
five strata. The outer layer, the stratum corneum, provides a protective barrier of dead cells that are tough and not soluble and that
are continuously replaced by new cells growing from below. It does
not contain blood vessels. The thicker dermis holds nerves, blood
vessels, and sweat glands as well as providing other functions. The
subcutaneous layer is essentially fatty. This complex layering has
many physical and chemical properties that change and evolve with
time (also see Figure 11.2).
Skin necessarily exhibits interesting mechanical properties in
its barrier- and shape-maintaining functions that derive from an
elastic collagen (long fibrous proteins) network. With time these
properties can change, usually leading to relaxations in stiffness
and tensions that in turn are manifest as “aging wrinkles” or flaccidness. With respect to light and optical phenomena, many kinds
of absorption properties exist at different layers that can again
vary with time. Chemical actions are equally remarkable. Needed
vitamin D, for example, is produced photochemically in the skin,
largely in the stratum basale and stratum spinosum layers of the
epidermis.
Nanoproduct Forms