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thumb|250px|right|Different bevels on hypodermic needles
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thumb|250px|Aiguille creuse hypodermique en gros plan.
Une '''aiguille hypodermique''' est une aiguille creuse, utilisée généralement avec une seringue, qui peut traverser la peau pour injecter des substances dans le corps. Elles peuvent également être utilisées pour prélever des échantillons liquides du corps, par exemple dans le cadre d'un prélèvement sanguin.

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A hypodermic needle is used when the substance would not be reliably absorbed by the digestive system, as is the case with drugs or if the substance needs to be instantly delivered into the body.  The substance can be injected just under the skin (intravenous injection). Less commonly, hypodermic needles are used for injection into joints (intra-articular injection), cerebrospinal fluid  (spinal injection- intrathecal) 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 HIV 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.

thumb|250px|right|Different [[bevels on hypodermic needles.]]
thumb|250px|right|[[Syringe on left, hypodermic needle with attached color-coded Luer-Lok&trade; connector on right.]]
A '''hypodermic needle''' is a hollow needle commonly used with a 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 for instant delivery of a drug, or when the injected substance cannot be ingested, either because it would not be absorbed (as with testosterone). There are many possible routes for an injection.

==Single use hypodermics==
Virtually all current hypodermic needles and their associated industrialized West, but in developing countries, such as in most of Danish surgeon in a rural hospital in Zaire in 1976. In this hospital, throwaway needles and gloves were a fantasy: needles and gloves were reused until obviously unusable. Although she was skilled in sterile procedure, she was often splashed with blood and other body fluids and may have accidentally suffered a needle-stick injury. Her story is told in Chapter 1 of ''And the Band Played On,'' by Randy Shilts.

Single-use syringes, which have automatic mechanisms to prevent reuse, have been developed to stop the spread of disease in medical settings, examples of which include medical-personnel exposure and immunizations.<ref>[http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/1998/10/27/MN52NEE.DTL&type=special DEADLY NEEDLES / Fast Track to Global Disaster<!-- Bot generated title -->]</ref> One type is a pre-filled plastic blister with a hypodermic needle attached via a one-way valve.<ref>[http://www.path.org/projects/uniject.php PATH: Uniject device<!-- Bot generated title -->]</ref>

==Manufacture==
Hypodermic needles are normally made from a stainless-steel tube drawn through progressively smaller dies to make the needle. The end is bevelled to create a sharp pointed tip. This lets the needle easily penetrate the skin. When a hypodermic needle is inserted, the bevel should be facing upwards.

==Needle gauge==
The diameter of the needle is indicated by the needle gauge.  Various needle lengths are available for any given gauge.  There are a number of systems for gauging needles, including the Stubs Needle Gauge, and the French Catheter Scale.  Needles in common medical use range from 7 gauge (the largest) to 33 (the smallest) on the Stubs scale. Twenty-one-gauge needles are most commonly used for drawing blood for testing purposes, and sixteen- or seventeen-gauge needles are most commonly used for blood donation, as they are large enough to allow red blood cells to pass through the needle without rupturing (this also allows more blood to be collected in a shorter amount of time).  Smaller-gauge needles will rupture the red blood cells, and if this occurs, the blood is useless for the patient that is receiving it. Although reusable needles remain useful for some scientific applications, disposable needles are far more common in medicine. Disposable needles are embedded in a plastic or aluminium hub that attaches to the syringe barrel by means of a press-fit (Luer-Slip&trade;) or twist-on (Luer-Lok™) fitting.

== Non-specialist use ==
Hypodermic needles are usually used by medical professionals&nbsp;&mdash; physicians, nurses, paramedics&nbsp;&mdash; but they are sometimes used by patients themselves. This is most common with type one diabetics, who may require several Benadryl and Decadron. The rapid injection of these drugs may stop a severe allergic reaction, prevent anaphylactic shock, and make an recreational intravenous drug use, for this reason it is illegal in many jurisdictions to possess used or unused needles without an approved medical reason.

== Industrial use ==
Disposable plastic syringes equipped with unbeveled blunt-tip Luer-Lok™ or Luer-Slip™ needles are often used in industry to apply precise amounts of lubricants, adhesives, and various other liquids and pastes.