Hair is one the most sensitive parts of the body--it reacts to changes in mood, environment and lifestyle. Most people will experience a change in their hair color when they are children and again when they are senior citizens. Genetics also plays a vital role in hair color.

Scientists are still unsure of why natural hair changes color. One theory is that certain genes in human DNA are triggered to start producing darker hair as adulthood approaches, and again to cease producing hair pigment altogether once the body starts to age. Another theory is that hair color reflects changing melanin levels, which adds color pigment to the skin and hair. As the body ages, melanin levels decrease, which may contribute to gray hair.

In July 2000, a Prague-based study called "Change in Hair Pigmentation in Children from Birth to 5 Years in a Central European Population" found that children of both sexes had a prevalence of dark hair within the first six months of their lives. From nine months to two-and-a-half years of age, the hair color in the children grew progressively lighter. It was noted that from three to five years of age, the hair began to darken again.

Scientists have linked external factors such as sun exposure, washing with alkaline soaps and frequent sea-bathing with natural hair lightening or darkening. Internal factors such as hormones and genetics also contribute to changes in natural hair color.