Input.GetMouseButtonDown no working

i have a get mouse button down script for an sprite for when i click the 2d sprite a level loads. I though it worked but it turns out everywhere i click i load the scene. How do i make it so when i click on the sprite on its own a scene loads.

     function Update () {
          if(Input.GetMouseButtonDown(0))
              Application.LoadLevel("1");
      }