Hypodermic needle

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For the theory on mass media effects, see Hypodermic needle model

Different bevels on hypodermic needles.

Syringe on left, hypodermic needle with attached color-coded luer lock on right.

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 for instant delivery of a drug, or when the injected substance cannot be ingested, either because it would not be absorbed (as with insulin), or because it would harm the liver (as with testosterone). There are many possible routes for an injection.

Virtually all current hypodermic needles and their associated syringes are designed for single use because they are hard to decontaminate and need 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.

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 [1] . One type is a pre-filled plastic blister with a hypodermic needle attached via a one-way valve. [2]

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.

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. 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) or twist-on (Luer-lock) fitting.