Chestnut hair is a shade of brown hair that has a slight reddish tone to it, and is often broken down into the two colors of chestnut brown or light chestnut brown hair. It is a brighter shade of brown than standard brown hair, but not as red in color as auburn hair, which has lighter and more easily visible red tones to it. Hair colors like chestnut hair can often be misidentified because there are many shades of brown hair in the population, which span a spectrum from golden brown colors to reddish hair, and browns that approach black in color.
The colors of hair in the human population tend to follow fairly distinct geographic regions, though brown shades such as chestnut hair can be common throughout the world. In Europe, in general, 60% to 80% of the population has light-colored hair in the Scandinavian countries of Iceland, Denmark, Norway, and Sweden. Much of the UK, as well as northern regions of Germany, Poland, and the Baltic states, including Finland, are also populated by largely light-colored hair such as varying shades of blond. Where chestnut hair predominates, it defines many border regions between these lighter hair populations and darker brown and black tones. This includes northern regions of Spain, southern regions of France and Germany, northern Italy, and more.
Since chestnut hair contains an element of red to it, populations such as those of the British isles and Ireland often have a significant number of people with chestnut shades of hair as well. This also tends to include Slavic regions of eastern Europe and northern areas of Africa and the Middle East. Like people with red hair, chestnut hair colors are often found on people who are have fairly pale skin and often blue, green, or gray eye colors. Darker versions of the hair color tend to reflect darker skin tones and brown eye color as well.
Hair color is known to be determined by two pigments in the body, and levels of these can alter as someone ages, resulting in the shade of his or her hair changing over time. Pheomelanin is the dominant pigment for conveying red hair color to individuals. Eumelanin can be of the brown or black type, and gives hair either a shade of brown or black color. The absence in the body or low concentrations of the brown version of eumelanin will result in blond hair colors, though this effect tends to fade with age and blond hair grows darker.