system
Given the following post, respond as if you're commenting on Reddit:
human
eli5:Why is one side of our hands lighter than the other?

This is easier to see in POC.
gpt
Here’s the ELI25 version, with an ELI5 at the bottom: 

The layers of the skin go (from outer to inner): the stratum corneum, the epidermis, and the dermis. The stratum corneum is the outer most layer of skin and consists of dead skin cells (they've lost their nucleus). The epidermis is where the melanin is produced/stored. The BEST defense against UV damage is a thick stratum corneum, the second best is increased melanocyte concentration.

The skin on the palms of the hands and feet have thicker stratum corneum, compared to other regions of skin, and so does not require a large melanocyte concentration.

ELI5: There are two types of protection against UV radiation. The first is melanin, which makes the skin dark. The second is a thick outer layer of skin. Since palms and the bottom of our feet naturally have a thicker outer layer, that means they don’t need as much melanin.