Hypodermic needles are medical instruments used to inject substances into the body or withdraw fluids. They consist of a thin, hollow tube with a sharp point at one end, allowing for easy penetration of the skin. These needles are commonly used for administering vaccines, medications, and drawing blood. The design of hypodermic needles varies in size and gauge, depending on their intended use. Smaller gauges are used for injections that require less discomfort, while larger gauges are used for drawing blood or injecting thicker substances. Proper sterilization is essential to prevent infections during their use.