ucts that elevate the SC water content. Indeed, one
French moisturizer has been reported that contains 83
ingredients.
Typical composition of
the stratum corneum
Well over 100 chemical compounds have been found
in the SC. Some formulators have felt it is useful
to enhance the concentrations of some of them by
including one or more in skin care products. On a
microscopic level, the SC does not have a uniform
composition from one part of its structure to another.
Consequently, the data in Table Two can be misleading
in some ways.
Typical emollients
A fairly large number of emollients are utilized in skin
care products (Table Three). The gold standard is
isopropyl myristate (IPM). Useful emollients are lipids
that are generally liquid, odorless, colorless, nonirritating
and very slow to evaporate. Esters are often
utilized. They must not impart a sensation of oiliness,
greasiness or stickiness. The rate of hydrolysis must be
negligible, since the released components might include
solids or irritating carboxylic acids. The natural
animal, vegetable or fish-based triglycerides (which
all contain unsaturated segments, like oleates) have
reduced oxidative stability. When the double bond is
attacked, odorous aldehydes and other degradation
compounds are formed, resulting in rancid odors.
There are ways to handle this problem, such as by hydrogenation and the use of antioxidants.
They are offered for commercial use in emollients and other products. Quite often, extra
amounts of surfactants must be used to emulsify these large molecules.
Quite often emollients are used in combinations. For instance, the widely-used petrolatum
forms an excellent barrier but is very oily and greasy. These adverse properties can be
reduced by adding myristyl benzoate or caprylic/capric triglycerides, which also improve
skin feel and moderate spreading ability. Myristal benzoate is also readily absorbed by the
SC.
Many emollients, such as ethyl and n.propyl myristate, are not used commercially due
to some drawbacks. The straight chain alcohol moiety makes the ester more subject to
hydrolysis than isopropyl and other branched chain esters. Others, like the “dimer esters”
are large, viscous and sticky molecules. Isopropyl palmitate (IPP), while less costly than
isopropyl myristate (IPM), is less preferred because of its slight irritant action.
Emollients are generally very safe to use. There may be some rare occurrences of allergic
contact dermatitis, irritational dermatitis or pigmentation disorders, but these are ephemeral
and of little consequence.
Typical moisturizers
If we characterize “moisturizers” as those conditioning compounds that reduce the
TEWL without forming a lipid layer on the skin, a number of examples cans be cited.
The simplest is water, especially if wetted by surfactants. Fingertip wrinkling is an
obvious effect, where so much moisture is absorbed that the SC can literally swell by
as much as 25% or more. The effect, however, is transient. A longer lasting one is
required. Glycerin has been used for thousands of years, with other diols and specialized
compounds added more recently. As mentioned earlier, their mode of action is only
partly understood and probably includes responses by both enzymes and genomes. Some
compounds are listed in Table Four.
Separate listings of emollients and humectants can be found in INCI volumes,
although some are not included and a number of compounds are unsuitable for dermal
hydration products.
40 Spray October 2018
Aquaphor
Ointment Body
Spray soothes
and relieves dry,
rough skin. The
cooling spray
is preservative-
and fragrancefree,
as well as
hypoallergenic.
Lindal provides
the aerosol valve
and actuator.
TABLE THREE
Typical Emollients
Some Commercial
Emollient Skin Conditioners
Isopropyl Myristate
Isopropyl Palmitat
C12-15 Alkyl Benzoates
C12-15 Alkyl Lactates
Di-PPG-3 Myristic Ether Adipate
Hexyl Laurate
Octyl Palmitate
Glyceryl Stearate Citrate
Shea Butter Ethyl Ester
Aloe Barbadensis Leaf Juice or equivalent
C8/C10 Triglycerides
Almond Kernal Oil
Steryl Heptanoate
Erucib Behenate
PPG-2 Myristyl Ether Palmitate
Sorbitan Isostearate
Cetyl Palmitate
Light Mineral Oils
Petrolatum