On fresh, young skin, freckles can look downright adorable. But once skin loses it youthful glow that cute little sprinkling of polka dots becomes something else entirely: nasty old liver spots. Whether you call them age spots, sun spots, lentigo, or just plain freckles, these uneven deposits of melanin are a variation on a suntan. In both cases, the increased production of brown pigment is our skin’s attempt to protect itself from the sun’s UV-B rays. Freckles are most commonly seen on fair-skinned people. Redheads and blondes are more likely to have freckles than dark-haired people, but many African Americans and Asians have them, too. In fact, when the Chinese-American actress Lucy Liu appeared in the movie Kill Bill with her freckles showing, she had trouble convincing people that they weren’t the handiwork of a clever make-up artist. Liu insists it’s the other way around—in earlier roles, a heavy layer of foundation masked the freckles she’s had since early childhood. So, is it our genes or the sun that causes freckles? The answer is both. UV-B radiation activates melanocytes—the cells that produce melanin. The distribution of melanocytes in our skin determines the presence or absence of freckles. In freckled skin, these cells are clumped together rather than spread out evenly. Very fair skin without freckles indicates that very few melanocytes are present. Freckles are also linked to the type of melanocytes you inherit. One type produces eumelanin, a black or brown pigment. In people with very dark, even skin tone, these cells are distributed evenly. The other type of melanocyte produces a yellowish or red pigment called pheomelanin. People who produce more pheomelanin than eumelanin will have freckles. The causes of the larger, darker discolored areas that often develop as we age are usually decades of sun damage, the increased melanin production that can occur as we grow older, or a combination of the two. In people of Northern European ancestry, the buildup of pheomelanin in the skin is associated with a defect in the melanocortin-1 receptor MC1R gene—a gene associated with not only your skin and hair color, but also your risk of developing melanoma. Recent scientific studies have also linked pale, freckled skin to a poorly functioning kit ligand gene, the gene associated with skin and hair color in East Asians. Now that we know where age spots come from, what can we do about them? In my next post, I’ll discuss the serious skin care regimen needed to reduce the visibility and roughness of the scaly brown splotches that can afflict aging skin.