About 2 yrs I noticed a small light brown patch developing on my lower back. I didn't think much of it, but in the past year I noticed more developing around the same area. They start small and faint and then over time grow larger and more pronounced in color, although no darker than a light brownish like a non-raised birthmark. The largest being about the size of a thumbprint.
What could these be?? What alarms me is that they're all on my lower back and have developed quite quickly.
I'm female and in my mid 20s, and I never expose my back to the sun.