Moisturization
Montfort A. Johnsen, Ph.D.
Technical Ed itor
The Key to Skin Beauty & Health
For thousands of years, people have been using vegetable oils to improve skin smoothness and
appearance. Still later, the hydrolysis (saponification) of these same oils was found to produce
an aqueous solution of what Swedish chemist Carl Wilhelm Scheele
discovered to be glycerol in 1779. It had profound skin hydrating and softening
effects. Today, glycerol is arguably our gold standard for skin humectancy.
Dry skin is technically a disease, primarily affecting the Stratum Corneum
(SC), the approximately 10% thick top layer of the human epidermis or skin.
Until about 1947, many clinicians incorrectly thought of the SC as the dead
outer cellular layer of the skin. They judged this mainly by examining the loose
or partly connected flakes and easily detached protuberances characteristic of
the “sandpaper texture” of dry skin. In fact, the bulk of the SC is in a layer
about 15 microns thick and bonded to the underlying Stratum Granulosa layer.
The SC consists of a large outer sub-layer and a smaller, thin sub-layer. Most of
the skin’s moisture content is concentrated in the top sub-layer. The SC is the
primary barrier for inhibiting and controlling the body’s water balance.
The moisture content of the SC should be a minimum of 10%, with normal
hydration ranging from about 18 to 36%. Dry skin (atopic dermatitis) may
contain as little as 3.4% moisture in the SC. There are approximations, noting that, for instance, the
SC of older people will contain significantly less moisture than the norm, inviting dry skin conditions.
During cold weather, the moisture levels in the SC will decrease due to low relative humidity conditions.
Within the SC, moisture is either tightly bound (by keratocytes): 0 to 7%, loosely bound: 7 to 35%
and free (remainder). These differentials act to prevent large swings of moisture content in the SC,
depending on weather, age, skin diseases and cosmetic or drug treatment conditions.
A particularly disturbing trait of dry skin is itching, whether sporadic or continuous. Itching leads
to scratching and skin desquamation. After scratching or rubbing the scaly, rough and partly peeled
SC will usually redevelop the itch, which may continue for 30 minutes or longer. Diseases such as xerodermatitus
atopic dermatitis and particularly prurititus can cause itching. In fact, itching is
generally known as prurititus. It usually relates to the activation of special nerves, known as C
fibers. They inform the brain of the problem. From about 60 to 90% of those with dry skin
suffer from various degrees of itching. Science has yet to develop an anti-pruritic treatment,
although naltrexone may temporarily suppress itching for some patients.
Aging and photo-aging can produce dry skin over time if it is left untreated. It can be evident
by roughness, scaling, loss of skin tone, appearance of mottled, red-brown pigmentation
spots, fine lines, wrinkles, micro-fissures a “sandpaper” texture on arms and legs and other
abnormalities. These pruritic inflammations and artifacts affect the corneocyte lipids, which
normally constitute about 15 volume percent of the SC and may be thought of as the “mortar”
between the stacked horny keratin filaments. They comprise the principal barrier and by
widening the filament separations, moisture loss is increased and more dry skin is produced.
The accompanying scales are generated by the action of “Kallinken 7” enzymes.
Transdermal Water Loss (TEWL)
The SC barrier function is deliberately incomplete. It must allow for perspiration, saline
removal, evaporative cooling in warm weather, the flushing of internal and external contaminants
(like dead cells) and so forth. Since the dermal area averages about 1.6 square meters,
these natural processes often go unnoticed.
The TEWL rate is typically about 5.5 grams per square meter per hour (g/m2/h). The
pH value was 4.8 at 70°F. During an eight hour sleeping period, the water loss would be
about 70g. (another significant amount would be lost through the mouth and nose). In some
contrast, people with allergic atopic dermatitis (xereroderm dry skin) experienced a TEWL of
30 Spray November 2017
Carl Wilhelm Scheele
Jergens Natural
Glow Daily Foaming
Moisturizer