What causes freckles on the human body?

Asked by: Sophie Webber, by email

Freckles are formed when groups of melanocyte cells beneath the skin are triggered by sunlight to increase melanin production. A regulating protein on the cells (called MCR1) is responsible for controlling this process. People who get lots of freckles have a variant of the protein that encourages greater production. The protein is coded by a dominant gene, which means that people who have freckles are highly likely to produce children who also get freckles.

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