melanocytes
'Melanocytes are like octopi with long arms. When the sun shines, they spread these out and deposit melanin in the skin. This protects the skin cells from sunlight. But over the years they become damaged and overproduce melanin, making a dark spot.'
"Melanocytes are like little factories churning out brown pigment granules, which is the pigment in our skin and they happen in a patchy way, rather than all over. If it happens evenly all over, you just get a tan right (but you're, hopefully, not tanning). But if it happens in a patchy way then you get blotchiness, and we all hate that. "

METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.