We often think that disposable razors mean just that: Use them a few times and toss them into the trash. The reason why disposable razors lose their sharp edge is water and humidity, which causes them to rust. If you want to extend the life of your razor, keep a wide-mouth jar filled with a few inches of vegetable oil in the bathroom. After shaving, rinse and dry the razor and place the head in the oil. This will prevent rust and keep the blades lubricated. You'll be surprised how long one razor can last.