You may consider the hood as another door of your vehicle. It is your entry point to gain access to the engine compartment of your front-engine vehicle. (The component is called a deck lid for rear-engine vehicles.)It consists of an inner and an outer panel. Composed of a one-piece frame of crisscrossing braces, the inner panel serves as the underbelly that supports the outer panel so it won't easily flex and get dented. The outer panel, on the other hand, is a metal sheet molded to fit and match the contours of the fenders and the top edge of the cowl. It shields the underhood systems from the rain, road debris, and any other element that should not be in the engine compartment.
Hoods come in different designs and styles. There are some whose undersides are covered with a sound-absorbing material to minimize the roar or noise that escapes the engine bay. There also those specially molded to accommodate special accessories, such as scoops. These are usually found on performance vehicles like SUVs, trucks, or sports cars. Very similar to air ducts in terms of form and function, scoops allow the engine bay to "inhale" and "exhale." Those installed facing the front end of the vehicle are able to "scoop" or channel outside air directly to the air filter, which improves the performance of the engine. But there are also scoops that have their openings facing backwards. Instead of taking in air, they're designed to vent hot underhood air, which also helps engine performance.
Now, whether your car hood is of the ordinary type or not, you probably know that you should do your best to keep it in good shape. You need not be told to avoid fender benders. But should you get into such accidents and your engine compartment lid got dented or scraped, repair the damage immediately. Fill and repaint deep scrapes filled and repainted, and level out dents before the hood's paint further cracks and causes rust. If you don't know how to do any of those, just have your local shop fix them for you.
If your hood starts to rattle when you drive, and it creaks when you open it, you would want to take a look at its hinges. Chances are these components are already rusty, lost a bolt or two, or have lost their proper alignment. For corrosion, it's recommended that you brush off the rust first with a rust remover and then apply white lithium grease on the hinges' pivot points to keep them well-lubricated for a long time.
Now if it's that huge piece of metal sheet that's already corroded so extensively you can remove chips of rust off it with your bare hands, then you probably got to get a replacement right away. For a good selection of painted or unpainted sturdy hood replacements, just browse Parts Train's catalog anytime.