The open end of the syringe may be fitted with a hypodermic needle, a nozzle or tubing to direct the flow into and out of the barrel.
Syringes are frequently used in clinical medicine to administer injections, infuse intravenous therapy into the bloodstream, apply compounds such as glue or lubricant, and draw/measure liquids.
The word "syringe" is derived from the Greek σῦριγξ (syrinx, meaning "Pan flute", "tube").
Two-part syringes have been traditionally used in European countries to prevent introduction of additional materials such as silicone oil needed for lubricating three-part plungers.
[3] Most modern medical syringes are plastic because they are cheap enough to dispose of after being used only once, reducing the risk of spreading blood-borne diseases.
Reuse of needles and syringes has caused spread of diseases, especially HIV and hepatitis, among intravenous drug users.
Syringes are also commonly reused by diabetics, as they can go through several in a day with multiple daily insulin injections, which becomes an affordability issue for many.
Even though the syringe and needle are only used by a single person, this practice is still unsafe as it can introduce bacteria from the skin into the bloodstream and cause serious and sometimes lethal infections.
[5] Medical syringes are sometimes used without a needle for orally administering liquid medicines to young children or animals, or milk to small young animals, because the dose can be measured accurately and it is easier to squirt the medicine into the subject's mouth instead of coaxing the subject to drink out of a measuring spoon.
An exception is the personal insulin autoinjector used by diabetic patients and in dual-chambered syringe designs intended to deliver a prefilled saline flush solution after the medication.
The most common types have a plastic nozzle which is placed over the affected area, and then the syringe piston is pulled back, creating a vacuum that allegedly sucks out the venom.
The dentist places the cartridge directly into a stainless steel syringe, with a double-pointed (single-use) needle.
In the UK and Ireland, manually operated hand syringes are used to inject lidocaine into patients' gums.
[29] In some jurisdictions, the sale or possession of hypodermic syringes may be controlled or prohibited without a prescription,[30] due to its potential use with illegal intravenous drugs.
Another application is to use the needle tip to add liquids to very confined spaces, such as washing out some scientific apparatus.
Glass syringes may also be preferred where a very high degree of precision is important (i.e. quantitative chemical analysis), because their engineering tolerances are lower and the plungers move more smoothly.
Used with a long needle or cannula, syringes are also useful for transferring fluids through rubber septa when atmospheric oxygen or moisture are being excluded.
Sometimes a large hypodermic syringe is used without a needle for very small baby mammals to suckle from in artificial rearing.