The connection between red hair and freckles is that they are both caused by the MC1R gene. This gene is basically responsible for the production of the MC1R protein, which is involved in the distribution of hair and skin pigments. Two major pigments affect people’s hair and skin, eumelanin and pheomelanin. People with freckles and red hair have more pheomelanin than people with other hair colors and non-freckled skin. The basic reason for this is that the MC1R gene either works — in which case it changes pheomelanin into eumelanin — or it doesn’t, resulting in a build-up of pheomelanin.
Genetics is basically the study of how traits are passed down in genes from the parents to the children. Each child gets two copies of each gene, one from the mother and the other from the father. Variations in things like hair color and eye color are related to genetics and can be explained through the different versions of each gene that can be inherited from parents. Both red hair and freckles can be caused by a version of the same gene, so people with that version of the gene are more likely to develop those characteristics.
Understanding the function of the MC1R gene is important to understanding the connection between red hair and freckles. The gene essentially tells the body how to produce the MC1R protein, which is responsible for managing the pigments in skin. Pigments are different chemicals which control the color of the skin, with eumelanin and pheomelanin being the two major ones. Pheomelanin is much rarer, and most people with a working MC1R gene convert it into eumelanin, resulting in most people having hair colors other than red. If the gene doesn’t work properly, then the pheomelanin accumulates, which causes red hair and the red appearance of freckles.
Freckles are caused by an unequal distribution of melanocyte cells within the skin. Most people have spread out melanocytes, which create the pigment responsible for skin color changing when exposed to the sun. People with a spread of melanocytes tan evenly, but people with clusters of them end up with concentrated spots of different color, called freckles. The MC1R gene can also cause the melanocyte cells to be clumped together in this way. This is why people with damaged MC1R genes often get red hair and freckles.
The reason some people have red hair with no freckles or freckles with no red hair is that they receive two copies of each gene, one from the mother and one from the father. If only one gene is broken, then the person can get clumps of melanocytes but no excess pheomelanin. In cases where both are broken, the person will get red hair and freckles.
