| A hypodermic needle is a hollow needle commonly used with a syringe
to inject substances into the body. They may also be used to take
liquid samples from the body, for example taking blood from a vein
in venipuncture.
A hypodermic needle is used when the substance would not be reliably
absorbed by the digestive system, as is the case with insulin and
many other drugs or if the substance needs to be instantly delivered
into the body. The substance can be injected just under the skin
(subcutaneous injection), into a muscle (intramuscular injection),
or directly into the bloodstream (intravenous injection). Less commonly,
hypodermic needles are used for injection into joints (intra-articular
injection), cerebrospinal fluid (spinal injection) or into the skin
itself (intradermal injection).
Virtually all current hypodermic needles and their associated syringes
are designed for single use because they are hard to decontaminate
and require sharpening after repeat use. Re-using or sharing needles
can transmit many blood-borne diseases including AIDS and hepatitis
C. Needles are normally used only once and disposed of in a sharps
container.
Normally made of stainless steel, the end of the needle is bevelled
to create a sharp pointed tip. This allows the needle to easily
penetrate the skin. When a hypodermic needle is inserted, the bevel
should be facing upwards.
The size of a needle is commonly stated as a gauge relating to
the outside diameter of the needle. Using the Stubs needle gauge,
these range from about 7 gauge (the largest) to 33 (the smallest).
Twenty-one gauge needles are most commonly used for taking blood.
The length of the needle is stated on the packaging and the gauge
is often indicated by the colour of the plastic connector (called
a luer).
There are a number of systems for gauging needles, including the
Stubs Needle Gauge, and the French Catheter Scale.
It is estimated that about 10% of the population may have a phobia
of needles.
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