Melanin

• Hair gets its coloring in the first place from pigments in our bodies called melanin. Without melanin, all hair would be white.
  
  

Types of Melanin

• Two types of melanin exist: dark (eumelanin) and light (phaeomelanin). The combination of these two pigments makes up the vast array of human hair color possibilities.
  
  

Genes

• Dr. Barry Star from Stanford University suggests that some traits built into our genes at birth, such as hair color, need to be "turned on." So while a child may have been born with light hair (heavy phaeomelanin levels), the child may have been genetically coded to eventually have more dark hair pigmentation (eumelanin).
  
  

Gray Hair

• Gray hair happens for much the same reason. As we age, melanin levels decrease in our bodies until we have insufficient amounts to color hair. It is a process predetermined by our genetics but also enhanced by certain external factors.
  
  

Other Factors

• Hair can also lose pigmentation and turn gray or white due to hormonal changes, or external factors, such as climate, air pollutants and exposure to chemicals.