Generally speaking, brightness, contrast, saturation and sharpness are thought to be the four simplest controls as they have been developed as long as the color TV was invented in the first place. However, people often turn blind eyes to the fact that all these four controls are related to each other. As a matter of fact, changing any one of these four controls will influence and change the other three.
People may tend to define sharpness as edge contrast, in other words, the contrast along edges in a photo. It is reasonable for people to have such definition. The fact is that an increase of sharpness will lead to the increase of the contrast between only along/near edges in the photo while the smooth areas of the image will not be influenced at all.
When you have made use of the tool of unsharp mask, you will only change the sharpness of the edges. In effect, different parts of the same image will show different change of their sharpness. As a matter of fact, where the edge is thicker, the sharpness will be increased while the contrast and brightness will not have obvious change at all. If the edge is rather thin, then the contrast, brightness and saturation will be greatly increased with the increase of the sharpness. Therefore, it is safe to conclude that increasing sharpness can cause the appearance of increase saturation, contrast, and brightness in areas of the image which contain fine detail where other areas (areas with broader detail) seem less affected except for the added sharpness. In all, changing one of these four controls really affects the other three most of the time. Keep in mind that you need to strike a balance between them; otherwise, the image will make people feel uncomfortable.