An injection is the act of administering a precisely determined quantity of a liquid substance into the body. The usual injection techniques involve the insertion of the needle below the surface of the skin, a method referred to as a subcutaneous injection. Injections may also be directed into a specific tissue or organ of the body. Injections may also be administered by intramuscular means (an insertion directly into a target muscle), intravenously (through a tube connected to the bloodstream that delivers predetermined quantities), or by needle-free injection technology.

The first hypodermic needles were developed in Europe in 1853; the term "hypodermic" is the combination of two Greek terms meaning "below the skin." The modern form of the plastic syringe was patented in 1959. The science underlying the hypodermic needle is simple: the hollow needle tube delivers the desired material into the body below the skin, where it will enter the cardiovascular system to be transported by the bloodstream to either a specific destination, or it will be circulated for a systemic benefit throughout the body.

In sports, injections are commonly used for the legitimate purposes of the administration of analgesics (painkillers) and anti-inflammatory medications such as cortisone, which are often injected directly into an affected joint. Injections are notorious in sport as the means for illegal and often dangerous substances consumed by athletes. The most common of these injections are those involving human growth hormones (HGH), some liquid compositions of anabolic steroids, and a variety of stimulants. Athletes taking such substances sometimes share the injection needle with a training partner, which creates a risk of disease or infection being transferred between the two users.

Former major league baseball All-Star Jose Canseco described how he and other noted ballplayers shared needles to inject one another with steroids in bathrooms and other nonsterile environments.

In some circumstances, the best hygienic practices give way to an emergency such as an anaphylactic reaction caused by an insect sting. In such cases, the administration of the medication, often by way of a pen-shaped needle containing antihistamine, must be performed as quickly as possible. In all other circumstances, proper procedure is often as critical as the injected substance to good long-term health.

Proper injection practices are designed to prevent the transmission of blood-borne diseases. The World Health Organization (WHO) estimates that every year approximately 25 million people worldwide are infected by a disease that was contracted by the person as a result of unsafe injection procedures. The most common of these transmitted diseases are hepatitis B, hepatitis C (both serious inflammatory conditions of the liver), and HIV/AID (the usually fatal disease of the immune system). Each of these diseases transmitted by unsafe injection is particularly dangerous because the blood-borne pathogens passed to the person have a delayed reaction within the body; the person may not have symptoms of infection for many months after the condition has become well established in the body. These diseases are highly contagious.

Another common outcome of a poor injection procedure is the development of an abscess, an infection occurring at the point of the entry of the needle into the body. An abscess will most often occur where the needle used was itself not sterile, or where the injection was performed in such a fashion as to create an opening in the surface of the skin that becomes infected. If left untreated, the abscess may either damage the skin, or it may permit bacteria to enter into the bloodstream from the infected area. This abscess may, in some circumstances, lead to the development of the poison blood condition known as septicemia, or sepsis.

The sharing of needles among one or more users is the most common unsafe injection practice. A safe injection procedure will ensure a reduction of risks for both the subject and the person performing the injection.

The hallmark of a safe injection practice is the use of a sterile, single-use syringe and needle, where the usage of which is restricted to one patient. If in the course of preparing for an injection the tip of the needle is touched by unprotected skin, the needle should be disposed of and a replacement needle used.

In addition to the quality of the needle, both the needle and syringe after use should be disposed of by way of a secure, puncture-proof container. The person administering the injection should ensure that his/her hands or any other part of the body that is

An injection ensures that a precisely determined quantity of a liquid substance into the body and can target specific tissue or a specific organ.
likely to come into contact with the recipient of the injection are thoroughly washed, or sanitized with alcohol or a similar substance, prior to injection.

All areas where infection might conceivably fester must be scrupulously clean. The administrator should wear disposable latex gloves during the administration of the injection. The surface of any place where the injection was administered (such as a training table) should be thoroughly cleaned, and any towels or coverings used should be washed separately. The opening in the skin should be swabbed with alcohol or a similar sterilizing agent, and covered with a bandage to ensure that no blood comes into contact with any other object after the injection.

Care must taken with the manner in which the syringe is filled with the substance to be injected. The person performing the injection must ensure that only the fluid, and not trapped air bubbles, are injected into the patient; the injection of air may cause a potentially fatal occurrence in the cardiovascular system of the subject.

When a person receives an injection on a regular basis, it is important for the health of the skin that the injection site be rotated among various locations on the body. The abdomen, upper arms, buttocks, and thighs are appropriate areas.

SEE ALSO Blood doping; First aid kits for sports; Glucocorticoids; Hormones.