The primary reasons dogs often have black lips are sun protection and genetics.
While the specific mechanisms can vary slightly between breeds, here's a breakdown of the key factors:
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Sun Protection: The dark pigmentation, specifically melanin, acts as a natural sunscreen. This protects the sensitive skin of the lips from harmful ultraviolet (UV) rays, preventing sunburn and potentially reducing the risk of skin cancer. This is particularly important in areas with less fur coverage.
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Genetics: Lip pigmentation is often linked to nose pigmentation. The genes responsible for producing black pigment are often dominant. Because lips and noses are both made from the same kinds of mucous-membrane cells, this often results in black lips. If a dog carries the gene for black pigment, it is more likely to express this trait.
In short, the black pigmentation on a dog's lips serves a protective function and is often a result of genetics, particularly the dominance of genes coding for black pigment production.
