St. Patrick's Day evokes thoughts of all things often associated with the Irish—including red hair. Chemically speaking, what sets redheads apart from the crowd is pigmentation—specifically melanins.
Most humans produce the brown-black eumelanin that results in varying shades of skin color and hair from blonde to black. Redheads have a genetic variant that causes cells to produce instead reddish pheomelanin, resulting in pale skin and fiery locks. How red hair is produced by redheads' cells might also explain why they have different sensitivity to pain.
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