Needles are used to inject medicines, vaccines, and other substances into the body, either under the skin, into a vein or directly into a muscle. A needle is also used for tattooing and, in many cases, piercings. Since the needle carries whatever is in it or on it directly into the body, it is important to make sure that it is as clean as possible. A sterile needle is one that has been treated with chemicals or heat to destroy all organisms on it. The accompanying syringe — the glass or plastic tube that holds the injectable substance and has the plunger to allow injection of the contents — must also be sterile for the sterile needle to be of any benefit.

People who inject themselves with street drugs are not always careful to use a sterile needle. Often they will use whatever is handy, even if it has not been kept clean. They also may share needles with other drug users, at that can be easier, and faster, than trying to find clean ones. Using needles that have been used by other people is a major cause of the transmission of such diseases as Acquired Immune Deficiency Syndrome (AIDS) and hepatitis. Some areas now have programs that provide sterile needles to drug users, to try to stop or at least to minimize the spread of these serious diseases.

A common household use for needles is for the removal of deep splinters and for opening blisters, boils, and sties. The needles used in these cases are almost always sewing needles. Pins, because of the type of metal from which they are often made, are usually a poor choice for these procedures. When people don’t take steps to make sure the needles they use are clean, serious infections may result. To ensure a sterile needle is being used, a person simply needs to soaked the needle in household bleach or alcohol for at least 15 minutes, to kill any bacteria or other contaminants that might be on it, then rinse the needle in clean water before use.

Glass syringes and reusable needles used to be common. These required meticulous cleaning and boiling to ensure sterility. Since the advent of plastic syringes and disposable needles, sterilization is rarely needed. A new, sterile needle and syringe is used every time, leaving no chance for the transmission of infection or disease. Any needles purchased from the pharmacy can always be assumed to be sterile — although the package should note it as well — and should be safe to use directly from the packaging.