22.0 g/m2/h, (pH value 5.6 at 70°F). The low ceramide and high TEWL of the diseased SC were responsible
for the dry skin condition.
The TEWL can be significantly reduced by two moisturizing therapies. In one, a lipid-based blocking
agent (like petrolatum) is applied as a topical film. In the other, a water soluble hygroscopic agent (like
glycerol) is applied, usually locally. Skin care products almost always use one of these approaches to sustain
or improve cosmetic appearance. The ingredients may be classified as humectants.
Another large class of skin care products is described as emollients. They act to soothe, soften, plump
and relax the skin, enhancing its appearance and tactile qualities. Combination humectant and emollient
products are very popular. They are offered as sprays, foams and lotions.
Lipid-Based Blocking Additives
Normal skin has about 45% water content. The water is slowly but constantly being added to the inventory
by the blood and other body sources. Meanwhile, water is being lost through evaporation, sweating and
(rarely) by a malady that discharges relatively large amounts through the palms and soles. Complex mechanisms
act to cause auto stasis, where gain and loss are balanced. Disturbances, such as various skin diseases
and aged skin syndrome, can cause an excessive TEWL, resulting in xerodermia (dry skin and ichythosis
vulgaris dermatitis) and other diseases. Preventative or corrective actions are needed.
White petrolatum is the most effective TEWL blocking agent known. Commercial products contain 60
to 70% complex mineral oil hydrocarbons and 40 to 30% mainly paraffins
plus microcrystalline waxes. It can reduce TEWL by 35%, while
similar lipids, like gelled mineral oil (23%) and mineral oil (15%) were
less effective. In normal skin, a two hour application of petrolatum
raised the skin water content from 45% to about 80%. Other petrolatum
functions include:
• Repairs the epidermal barrier
• Coats the SC but does not permeate it
• Can act as a ultra-violet (UV) screening agent
• Can act as a microbicide for aerobic organisms
• Can kill most bacteria
• Reduces the possibility of dermatitis in infants
• Reduces the possibility of skin abrasions, cuts and bruises
• Provides dermal lubricity
• Helps control xerotic eczema
• Has analgesic properties
• Is odorless, tasteless, essentially colorless and chemically stable
• Is commercially available in gels (jellies) and liquid forms.
Another lipid film forming occlusive blocking agent is lanolin.
Derived from sheep, the raw material is extremely complex, with
about 11,000 ingredients thus far identified. Various esters account
for about 90%. Alcohols are typically present at over 9%, while the
remainder consists of complex hydrocarbons and fatty acids. Lanolin (melting point 104°F) is an outstanding
Vaseline Spray & Go aerosol moisturizer comes
in Total Moisture, Cocoa Radiant and
Aloe Fresh scents.
lubricant and moisturizer. It produces TEWL reguctiona about 50 to 70% as high as petrolatum. Some
antimicrobials are present in lanolin, preventing rancidification in containers or on the skin, but waterbased
emulsions should be preserved by the inclusion of 0.2 to 0.5% germicides.
Hundreds of lanolin derivatives are currently marketed. Due to their complexity, one “Lanolin Alcohol”
may not be the same as another “Lanolin Alcohol.” Often the difference can be obscure, like variation in
the slight ability of the product to penetrate the SC. Years ago there were variations even within commodity
brand names, but this has been corrected by suppliers.
Many people bathe daily and wash their hands several times each day. The soaps and syndets are designed
to emulsify and remove skin lipids. As such, they virtually eliminate cholesterol and its lower homologs,
fatty acids (up to about C20) and disperse even small amounts of ceramides. The typical 15% water content
of the SC rises several-fold during bathing, but then quickly drops to the 8 to 12% dry skin level by temporary
desiccation. This has inspired some formulators to include these chemicals in moisturizing or skin
conditioning products. Similarly, since chemicals like urea and hyaluronic acid (HA) are found in the SC,
they have become ingredients in some skin care products.
Hygroscopic Obtrusive Additives
The best known agent for this form of SC moisturization is glycerol, or more technically, 1,2,3-trihydroxypropane.
Although known for hundreds of years, its first use as an aerosol moisturizing agent probably
November 2017 Spray 31