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 the intended use. Smaller gauge numbers indicate thicker needles, while larger numbers indicate thinner ones. They are often used in conjunction with syringes to deliver precise doses of medications or to collect samples for laboratory testing.