Salon Fundamentals
TM
Esthetics
s k i n p h y s i o l o g y
268
The sebaceous glands originate in the dermis,
open onto the surface of the skin, and produce
and release sebum to condition the
surrounding skin. Sebum mixes with the
secretions of the sweat glands, creating a layer
of oil and moisture called the acid mantle,
located in the epidermis. When the pH
(potential hydrogen; see Chapter 7, Chemistry)
of the skin is measured, it is actually the acid
mantle that is being identified, which has a
natural pH of 4.5 to 5.5. The acid mantle
protects the skin from bacterial invasion by
creating an acidic environment that is hostile
to bacterial growth.
Besides the sudoriferous and sebaceous glands,
other appendages (extensions) of the skin include
the hair and nails. Hair follicles cover the entire
body except for the palms of the hands and soles
of the feet. Hair growth rate increases with
androgen production, particularly on the trunk
of the body. The amount of hair on the body
depends on genetics and hormonal changes.
Hormones also affect the thickness and quantity
of hair on the scalp and face, particularly in
women during menopause.
Eccrine glands are primarily responsible for
thermoregulation, or lowering body temperature.
If the body overheats, large quantities of sweat are
secreted onto the skin's surface.
Sebaceous glands continually produce and
secrete sebum, a complex mixture of fatty
substances. Also known as oil glands, they are
located in the dermis and are distributed all over
the surface of the body except in the palms of
the hands and soles of the feet. The largest
number of sebaceous glands is found on the
forehead, nose and back. Sebaceous glands are
attached to the upper third of a hair follicle and
are two to three times larger around facial hair
follicles than they are around scalp hair follicles.
This is why breakouts tend to happen more
often on the face rather than the scalp. The
amount of sebum produced by the sebaceous
glands is influenced by androgen, a male
hormone present in both men and women.
It is common to find larger sebaceous glands
in men than women. Sebaceous glands, in
addition to sudoriferous glands, are considered
appendages of the skin.
Adult skin contains two to five million sweat
glands, with the palms of the hands and soles
of the feet having an estimated 500 sweat
glands per square centimeter.
·
Sebaceous gland
(oil gland)
·
Sudoriferous gland
(sweat gland)
·
Subcutaneous layer
(body's cushioning)
You have probably noticed that when it is cold, you
get "goosebumps." Goosebumps are caused by the
contraction of arrector pili muscles that are connected
to each hair follicle. When the muscle contracts, it
causes the hair to stand on end. This "tents" the skin,
with the hair in the center of the bump. Arrector pili
muscles also push sebum from the glands toward the
openings of the hair follicles. In most mammals, the
arrector pili muscles contract reflexively in response to
cold to increase the thickness of the insulating "coat."
