The next time you get a burn on the back of your hand, it will afford you an opportunity to see cytokines at work. After the burn heals, you will notice that surrounding the burn, the skin begins to form a dark ring of melanin around the burn area.

The reason the ring is darker than normal is because the burned skin is sending out cytokines asking melanocytes to produce melanin for UV protection. However, the only functioning melanoytes are on the periphery of the burn, hence, the ring.