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Anyone who has spent enough time doing dishes, soaking in a hot
tub, or swimming in a warm pool has seen the skin in their fingers and
toes become white and wrinkly. This phenomenon is sometimes called
pruning, or water aging. When this happens, the skin tends to appear
puffy, and lose much of the sensation that it normally has –
particularly the fingertips, which are normally very sensitive. When
the skin is no longer immersed in water, it begins to return to normal,
and soon, there are no signs of the wrinkly, puffy skin that was there
earlier. Though it is a common occurrence, and one to which we normally
don’t give much thought, scientists are still at odds over the
explanation for this phenomenon.
Human skin is comprised of three layers. The deepest layer is called
the subcutaneous tissue, which contains fats, connective tissue, nerves
and large blood vessels. The middle layer is the dermis, which
contains the hair follicles, more nerves, smaller blood vessels, and
sweat glands. The top layer, the epidermis, is the layer which protects
the underlying layers from harm, and helps to regulate water
evaporating from the body. There are four layers in the epidermis, the
topmost of which is the stratum corneum. This is the layer which is
visible, and which contains keratin, a protein which is present in
fingernails and hair.
The epidermis is capable of absorbing large quantities of water, but
usually doesn’t because the skin is covered with an oily substance
called sebum. It is this substance which leaves an imprint behind when
you touch something, and creates fingerprints on surfaces. After
prolonged periods of time in the water, much of the sebum is washed
away, which makes the skin more prone to absorbing water. This is why
skin doesn’t start to wrinkle right away when it’s submerged in water,
but takes some time to do so. It is also thought that sebum is produced
in areas where there is a concentration of hair, and the fingertips,
palms of the hands and feet typically lack any hair, so there is less
sebum there to prevent the skin from absorbing water.
It is thought that the toughness of the outer layer of skin is due to
the keratin present therein, and that it is the keratin which prevents
the skin from swelling uniformly when it is submerged. As a result, the
increased surface area of the skin causes it to wrinkle. The reason
why the wrinkling affects the hands and feet, but not other areas of the
body, is that the fingertips and bottoms of our feet have the thickest
skin, and the highest concentration of keratin. Another theory is that
because the epidermis is connected to the dermis in some spots, but not
everywhere, the spots that are not connected tend to swell more; as a
result, some areas of the skin swell more than others, producing the
wrinkle effect.
Some scientists have also linked the effect of water-related
wrinkling to a process called vasoconstriction. This theory posits that
the nervous system plays a role in the wrinkling process. In 1935, two
doctors named Lewis and Pickering studied patients with palsy of the
median nerve, and noticed that water-related wrinkling did not occur in
areas of the patients’ skin which were normally innervated by the
damaged nerve; as a result, they drew the conclusion that the phenomenon
of water aging could not be explained by simple water absorption alone,
but that the sympathetic nervous system played a part in the process as
well. This theory, however, has not been completely proven. Regardless
of the reason for the wrinkling or pruning process, the skin returns to
normal after some time out of the water, and it appears that there are
no adverse effects, aside from cosmetic concerns.
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