342 JOURNAL OF COSMETIC SCIENCE
bound to SC cell envelopes from the ventral forearms of Japanese subjects in their 20s, 30s,
40s, and over 50. Total bound ceramides were lower in Autumn and Winter compared
to Spring and Summer for all ages but a significant decrease in total bound ceramides in
the over 50 age group compared to younger ages was only observed in the Spring. On the
other hand, confocal Raman microscopy results from Choe et al.64 indicate no significant
difference in the amount of intercellular SC lipids in subjects averaging 29 years old and
those averaging 50 years old. They did report higher ordering of intercellular lipids in the
intermediate levels of the SC in the older subjects.
AGING AND EPIDERMAL BARRIER FUNCTION
The most common and best validated method for determining SC barrier function in vivo
is by measurement of TEWL, the passive diffusion of water through the skin.65–67
Varying results have been reported by several groups who studied the effects of age on
SC barrier function by measuring TEWL. In a recent study Luebberding et al. reported
TEWL data from 6 different body sites on 150 women.68 TEWL on the décolleté area was
positively correlated to age, ranging from 5.62 gm/m2-hr on the youngest group to 7.86 gm/
m2-hr on the oldest with a high level of statistical significance but they reported a negative
correlation to age on the forehead and cheek and no correlation on the neck, forearm, or
back of the hand. Conversely, Pan et al.69 reported a positive correlation between age and
TEWL on the forehead of 178 women ranging in age from 20 to 64, but also reported a
negative correlation on the cheek. Wilhelm et al.70 found significantly lower TEWL with
advancing age, and five additional studies showed a trend toward lower TEWL with aged
Figure 3. Projected corneocyte surface area for two age ranges for men (⚫) and women (⚪). Reprinted from
Grove et al.56 with permission of the Society of Cosmetic Chemists.

343 Aging Skin Barrier
skin compared to younger subjects (Marks et al.,71 Kligman,72 Leveque et al.,25 Saijo et al.,73
Ghadially et al.85). See Table 1.
Hillebrand and Wickett74 reported TEWL data collected by G. Hillebrand, from 452
Chinese women between the ages of 10 and 70 years. ANOVA reveals statistically significant
differences between grouped ages (p =0.008). The 10–19 age group mean is significantly
less (p 0.05) than the 30–39, 40–49, and 50–59 age group means. The 60–70 age group
mean was also significantly less than the 30–39, 40–49, and 50–59 age group means. The
authors stated, “With these data, expressed in this way, we might conclude that skin barrier
function on the forearm of Chinese women living in Beijing decreases from the teens to the
forties (as gleaned from the 17% increase in TEWL) and thereafter increases.” However, the
authors also presented a scatter plot of the data showing all the individual data (Figure 4).
As the authors point out that while detailed statistical analysis indicates that TEWL is
lower in the 10–19-year-old age group, increasing in the 30–59-year-old age groups and
decreasing again in the 60–70-year-old age group the scatter plot indicates that there is
little or no clinical significance in these differences. Table I summarizes the effects of age
on TEWL reported by various authors.
Akdeniz et al.77 performed meta-analysis of 212 studies of TEWL primarily from the
forearm published between 1947 and 2017. The authors concluded that TEWL either does
not change or decreases slightly with age in general agreement with the studies discussed
above.
Possible age-related changes in skin penetration of organic compounds have been
investigated. Roskos et al. compared penetration of six drugs of differing polarity into the
skin of subjects 22–40 years of age and over 65 years old in vivo.78 Permeation rates for the
two most hydrophobic drugs, testosterone, and estradiol were not significantly different
between the two age groups but hydrocortisone, benzoic acid, acetylsalicylic acid, and
caffeine penetrated the skin of the older subjects at a significantly lower rate than younger.
Rougier et al. also reported that benzoic acid penetrated older skin significantly more
slowly than younger in vivo.27
Analysis of all these results leads to the somewhat surprising conclusion that basal SC
barrier function is relatively unaffected by age from childhood through late middle age
and then may begin to increase slightly sometime after age 60. It is notable that this
apparent improvement in baseline barrier function occurs in spite of the possible reduction
in SC barrier lipids discussed above. Rogers et al. point out that while lipids decrease
the ratio of ceramides to other SC structural lipids remain approximately constant.60 It is
also possible that skin permeation of some compounds through SC is slower because of
increased corneocyte area (see above). Rougier at al. found a negative correlation between
corneocyte size and the skin permeation rate for benzoic acid in vivo.27
AGING AND SENSITIVITY TO IRRITANTS
Most studies indicate that the reactivity of skin to irritants tends to decrease or at least does
not increase with age as one might expect. Bettley and Donoghue reported fewer reactions
to patch testing with soap in subjects 50 and older compared to subjects 10–49 years of
age.79 Grove et al. reported lower skin reactivity to a variety of irritants including dimethyl
sulfoxide, ethyl nicotinate and lactic acid in older subjects.56,80 Maibach and coworkers81,82 and
Robinson83 observed lower reactivity of older skin to sodium lauryl sulfate (SLS). Robinson