There is also vitiligo, which is a loss of pigment. I believe that it is from an immune system disorder, but does not make one sick - simply causes the loss of pigmentation. It will often show up around the mouth, on the hands, and in the groin area before showing up in larger areas. Often it exists and the person doesn’t know they have it.
One way to examine yourself for hyperpigmentation, hypopigmentation, or vitiligo is to view your skin under a black light. Most people will be surprised to see how much blotchy pigmentation they have as well as areas with no pigmentation. One of my colleagues discovered that she had vitiligo (later diagnosed) when she began collecting vaseline glass (it’s green and glows under black light). I’m sure other electrologists notice areas where clients lack pigmentation, however, we do not diagnose, and why bring something to their attention if it is not noticeable to the naked eye.
Make-up should smooth out any uneven skin tone.