Peter Lio, MD
Posted: 06/20/2011
"Smooth as a baby's bottom" summarizes the popular notion of infant
skin: the soft, supple, and practically flawless integument that is the
unattainable objective of all cosmetic treatments. Indeed, it can be
difficult to imagine what problems a pediatric dermatologist could
possibly address given how perfect newborn skin appears to be. And while
there are undoubtedly plenty of skin maladies that affect those at the
beginning of life, even for the smoothest of bottoms, there are critical
differences worth thinking about, both in health and disease. In this
article, we review some of the important structural and physiologic
differences between infant (defined here as the first few years of life)
and adult skin. We also consider some of the clinical and practical
ramifications of these distinctions using evidence whenever possible.
The functions of the skin remain essentially the same at all phases
of life, including: barrier, photoprotection, thermoregulation, immune
surveillance, hormonal synthesis, insensible fluid loss prevention, and
sensory perception.
However, there are several important structural differences between
the skin of babies and adults, differences immediately accentuated as
the newborn transitions from the intrauterine environment to the outside
world.
Barrier function of the skin is vital for survival for all human
beings. With increasing prematurity, there is increasing barrier
dysfunction with higher transepidermal water loss (TEWL) and increased
percutaneous absorption of chemicals.
As a result, there is greatly increased mortality in premature infants
with impaired barrier function, generally due to microbial invasion.
Remarkably, this can be demonstrated experimentally by application of
emollients that enhance barrier function. In a randomized, controlled
trial, massaging premature infants with sunflower seed oil 3 times daily
resulted in a 41% reduction in sepsis and a 26% reduction in mortality.
Although the TEWL in full-term infants is generally agreed to be close to that of healthy adults, there is recent evidence that the barrier development continues during the first year of life.
Infant skin is found to have higher water content and is able to absorb more water and lose excess water faster than adult skin.
Other microstructural differences include thinner stratum corneum and papillary dermis in infant skin.
Beyond these structural points, however, several factors converge to
make
infants more susceptible to percutaneous toxicity.
Their high
surface area-to-volume ratio, immature drug metabolism systems, and
decreased subcutaneous fat stores effectively increase the absorptive
area while decreasing the volume of distribution of a drug or toxin.
This is compounded by the fact that once absorbed, the infants lack
fully developed drug carriage and detoxification systems.
Furthermore,
direct barrier injury can occur because of the increased fragility of
infant skin, particularly from the removal of adhesive tapes and
monitors, thus increasing local permeability.
Finally, given the estimated 20% incidence of atopic dermatitis among children,
there are yet other reasons for barrier function to be impaired at
baseline.
Because of these factors, it seems prudent to advise that
only
essential products be applied to the skin, particularly in the first
several months of life.
Below the skin, in the subcutaneous fat, there are also discrepancies
between mature and immature. In newborns, the subcutaneous fat is rich
in the saturated oils palmitic and esteric acid. These fats have higher
melting point temperatures than the increasingly unsaturated fats of
adulthood; as more oleic acid becomes present, the melting point
diminishes.
The higher melting point means that the fat in infants can freeze more
easily: approximately 64°C vs the much lower adult melting point of
14°C.
This principle is typified by "popsicle panniculitis," a fairly common
form of fat necrosis in the cheeks of infants several hours after eating
popsicles or ice, and the closely related equestrian panniculitis, seen
after the cold exposure from riding horses, bicycling, or riding
motorcycles.Subcutaneous fat necrosis of the newborn, a condition frequently
associated with hypothermia, trauma, or other perinatal stressors, is a
panniculitis that may also be related to the higher melting point of
infant fat.
Because of this limitation in infant skin, extra care must be made to avoid temperature extremes.
Bathing an infant provides important psychological benefits between parent and child.However, oddly enough, it can also provide an opportunity to damage the
skin. There is evidence to suggest that washing the skin with a
washcloth during the first 4 weeks of life is associated with increased
TEWL and decreased stratum corneum hydration compared with simply
soaking in water.
Another study found that tub bathing an infant was actually associated
with an increased risk of cord infection vs no washing at all.
Several papers have examined the use of mild liquid cleansers vs using
water alone for bathing. The consensus appears to be that a mild liquid
cleanser may actually be less drying and less irritating than water
alone, and that bathing should be brief (10 minutes or less) and no more
than every other day with spot cleaning in between.
Photoprotection is an important function of the skin, though in the
process of preventing ultraviolet (UV) sun damage to certain structures,
the skin can itself accrue damage, increasing the chances of skin
cancer. As for adults, sun protection is important in childhood. This
topic takes special importance because the damage from UV radiation is
cumulative: children spend more time doing outdoor activities, younger
skin is more susceptible to damage, and UV damage in childhood may have
particularly profound consequences later.
It is also important to remember that infants are entirely dependent
upon their caregivers to practice sun protection and are generally not
able to communicate the symptoms of early sunburn.
In recent years, concerns have emerged over possible
hormone-disrupting chemicals in sunscreens, such as oxybenzone.
In
children, the doubly worrisome scenario of increased percutaneous
absorption of chemicals and the enhanced developmental sensitivity to
hormone disruption makes this topic extremely contentious.
Evidence for
such absorption is fairly abundant with 1 study concluding: "...whilst
limited absorption across the skin was observed for the majority of the
sunscreens tested, [oxybenzone] demonstrated sufficiently high
penetration to warrant further investigation of its continued
application."
Evidence for hormone disruption is another issue that is well
established for benzophenone-3, homosalate, 4-methyl-benzylidene camphor
(4-MBC), octyl-methoxycinnamate (OMC), and
octyl-dimethyl-para-aminobenzoic acid (PABA). All show estrogenicity,
and studies document environmental persistence and widespread presence in the population.
Unfortunately, even the mineral sunscreens such as titanium dioxide and
zinc oxide are not without risk. There is evidence that the
nanoparticles present in many of these mineral sunscreens can cause
cellular damage.
Although most studies have shown that there is minimal penetration into the skin,
no studies have yet tested these particles in fragile or damaged skin.
Infant skin is more fragile, and with the incidence of atopic dermatitis
approaching 20% in some populations, there is a reasonably high chance
that there will be areas of skin damage in some infants.
My conclusion strongly reinforces the message conveyed by the American
Academy of Pediatrics: minimize the reliance on topical products in
infancy by avoiding sun exposure and using sun-protective clothing
whenever possible.
Skin diseases in infants and adults can vary as much as the
difference in fundamentals of the skin. Even disorders that may sound
familiar from experience in older patients may be distinct in infants:
acne, skin infections, and nutritional dermatoses, to highlight a few.
Classical teenage acne (acne vulgaris) is well known to all of us;
however, there are 2 distinct forms of acne that can affect patients in
the first few years of life: neonatal acne and infantile acne. Neonatal
acne is perhaps more accurately referred to as neonatal cephalic
pustulosis (NCP) and can affect up to 20% of newborns.
This papulopustular disorder lacks the comedones of true acne and may
actually be related to colonization with Malassezia yeast species on the
skin. Generally benign and self-limited, treatment with topical
ketoconazole may shorten the duration of the disease.
Infantile acne, on the other hand, is far more rare than neonatal acne, and generally occurs between 3 months and 1 year.
Both comedones and inflammatory papules are seen in this disease, and
like its teenage counterpart, scarring may be an issue. Sometimes
infantile acne will resolve by school age without specific treatment,
but it may also be a harbinger for severe forms of acne in adolescence
and appears to be more common in families with a strong family history
of acne.
Here the differences end: treatment can be very similar to that for
teenage acne, including a topical retinoid and topical benzoyl peroxide.
[25]
Staphylococcal scalded-skin syndrome in infants and children is
caused by staphylococcal bacteria that release exfoliative toxin and can
also be seen in adults with renal failure. This suggests that it is the
inability to clear the toxin that causes the characteristic superficial
bullae and widespread sloughing, with crusting and impetiginization at
the orifices.Prompt diagnosis and treatment with systemic antibiotics and skin
barrier support are necessary to minimize morbidity from this disease.
Infants are also particularly susceptible to nutritional
deficiencies, and zinc deficiency may be acquired or inherited.
Acrodermatitis enteropathica (AE) is the rare, autosomal-recessive
disease of impaired zinc absorption that usually presents upon weaning
from breast milk.
Acrodermatitis enteropathica-like eruption can be seen in the setting
of insufficient dietary zinc, including breast milk deficiency.
Symptoms of periorificial dermatitis, diarrhea, and hair loss
frequently are mild and incomplete, making this disease a challenge to
diagnose at times. Once the diagnosis is made, zinc supplementation is
required, which generally results in dramatic reversal of skin lesions
within several days.
Infant skin is often thought of as ideal skin, and its
characteristics are frequently sought by adults. However, beyond the
smooth and supple beauty, there are significant structural and
functional differences that make infant skin more susceptible to certain
problems. During the first years of life, there are considerable
developments of the skin and subcutaneous fat that warrant handling
infants differently—and much more gingerly—than adults.
http://www.medscape.org/viewprogram/32035?src=0_mp_cmenl_0
source : Medscape Pediatrics