A characteristic of particular bacteria
(especially those responsible for tuber-
culosis) that are resistant to the acids
used to dye specimens for microscopic
A disturbance of the body’s
in which there is an accumu-
lation of acid or loss of
There are two types of acidosis: meta-
bolic and respiratory.
amount of acid is produced by meta-
bolic processes. One form of metabolic
acidosis is ketoacidosis, which occurs in
vation. Metabolic acidosis may also be
caused by loss of bicarbonate (an alkali)
as a result of severe diarrhoea. In
there is insufficient excretion of
acid in the urine.
breathing fails to remove enough car-
bon dioxide from the lungs. This causes
increased acidity of the blood because
the excess carbon dioxide remains in
the bloodstream, where it dissolves to
form carbonic acid. Impaired breathing
leading to respiratory acidosis may be
caused by chronic obstructive pulm-
onary disease (see
The regurgitation of acidic fluid from
the stomach into the
tube that connects the throat to the
stomach). Acid reflux is the result of
inefficiency of the muscular valve at the
lower end of the oesophagus.
Also known as
reflux disease (GORD), acid reflux may
inflame the oesophagus, resulting in
(a burning pain in the chest)
Mild acid reflux is common but is
not serious. It may occur during preg-
people. Repeated episodes of discom-
fort may indicate a
which part of the stomach protrudes
into the chest).
A chronic skin disorder in which there
is inflammation of the
at the base of hair follicles in the skin.
help to keep it under control. Over-the-
counter topical drug treatments such as
benzoyl peroxide or azelaic acid are
often effective. Prescribed topical
or retinoic acid (a derivative
are used to treat moderate
acne. Alternative treatment is with oral
very severe cases,
given under hospital supervision. In
all cases, exposure to ultraviolet light
(either natural or artificial) may also
be beneficial. However, it is important
not to burn the skin.
Acne improves slowly over time, and
it often clears up by the end of the
The most common type of acne is
known as acne vulgaris,
which almost always develops during
puberty. Chemical acne is caused by
exposure of the skin to certain chemi-
development of acne in areas where
the chemical has come into contact
with the skin, such as on the thighs.
Certain prescribed drugs, such as
can also cause acne.
The spots on this boy’s face are typical of acne;
the darker marks are healed spots, which fade
gradually. Severe acne may leave pits in the skin.
Acne spots are caused by the obstruc-
tion of hair follicles by excess sebum
(the oily substance secreted by the seba-
ceous glands). Bacteria multiply in the
monal changes at puberty, including
increased levels of
(male sex hormones) in both males and
females, stimulate the production of
sebum. There may also be a genetic pre-
disposition to acne.
Acne develops in areas in which there
is a high concentration of sebaceous
glands, mainly the face, centre of the
around the neck. Milia (whiteheads),
comedones (blackheads), nodules (firm
swellings under the skin), and cysts
(larger, fluid-filled swellings) are the
most common types of spot. Some, par-
ticularly cystic spots, leave scars.
TREATMENT AND OUTLOOK
is no instant
cure for acne,
although washing the affected areas at
least twice a day with a mild soap may
The part of the
(the eighth cranial nerve) concerned
with hearing. The acoustic nerve is also
called the auditory or cochlear nerve.
A rare, noncancerous tumour arising
from supporting cells that surround the
the internal auditory meatus (the canal
in the skull through which the nerve
passes from the inner ear to the brain).
CAUSE AND INCIDENCE
occur in people between the ages of 40
and 60 and are slightly more common in
women than in men.
Usually, the cause of an acoustic neu-
roma is unknown. However, tumours
that affect the nerves on both sides of
the head simultaneously may be part of
ease characterized by changes in the
nervous system, skin, and bones).
An acoustic neuroma can cause
(noises in the ear), loss of bal-
ance, and pain in the face and the
affected ear. As the tumour enlarges, it
may lead to additional complications,
(loss of coordination) due
to the compression of the brainstem
DIAGNOSIS AND TREATMENT
Diagnosis is made by
(techniques that produce cross-section-
al or three-dimensional images of body
Surgery may be necessary to remove
an acoustic neuroma, but treatment
also be effective.