Changes in hormone levels can cause pigment genes to be turned on or turned off. This can happen in adults too! … Changes in age, nutrition, temperature, sun exposure and various other factors can cause our bodies to change the amounts or types of hormones we make. Some animals change their hair color twice a year!
What causes hair to be different colors?
Hair color is determined by the amount of a pigment called melanin in hair. An abundance of one type of melanin, called eumelanin, gives people black or brown hair. An abundance of another pigment, called pheomelanin, gives people red hair. … The best-studied hair-color gene in humans is called MC1R.