Why Does Hair Color Change in Children?

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As children grow and develop, their physical appearance constantly changes. Faces become slimmer; features become more defined; bodies fill out and become taller. These changes are expected. But sometimes, a child’s hair color can undergo a startling transformation. Although it’s fairly common for hair to darken over time, black hair might become blonde, and brown hair might become red. Usually a change in hair color has a natural cause, but sometimes it indicates a more serious issue.

A toddler combs her hair.
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Like other physical traits, hair color is determined by genes received from both parents. Unlike other genes (except for those that affect eye color, which work the same way), genes that control hair color can be ignored or turned off. An ignored or turned-off gene for blonde hair will lead to brown or black hair. Conversely, dark-haired parents might be surprised by blonde babies. Aside from these extremes, it’s also possible for hair color genes to be turned on at varying degrees, like a dimmer switch on a light bulb. Scientists don’t know why hair color genes are sometimes dimmed or ignored. They do know that a kind of protein called a transcription factor turns the genes on or off. Eventually, the genes are turned on completely, and the true hair color is revealed (see Reference 1).

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Darker hair is the result of higher levels of melanin, a dark brown pigment found in skin, eyes and hair. Because children have less melanin than adults, they are more likely to have lighter hair. As they mature, these levels increase and make hair darker (Reference 2). Increasing hormone levels can also cause hair to darken during puberty (Reference 3).

An older brother plays with his young siblings outside.
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Hair turns gray from a decreased production of melanin. Children as young as 8 years old can begin turning gray because of an early onset of this reduction (see Resources). However, gray hair can be caused by a deficiency in Vitamin B12. It can also indicate illness, such as anemia, thyroid disorders or osteoporosis. Systemic diseases, such as HIV, can sometimes change hair color, and so can malnutrition .For these reasons, prematurely graying hair should always be investigated by a physician (Resources).

A pediatrician hands a prescription to a mother and child.
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Hair that becomes lighter in portions of the overall length might indicate ingestion of thallium or boron salt. Both substances are poisonous (Resource 8 in Additional Resources). Thallium is a mineral found in soil and sometimes food (Resource 9, Additional Resources). Boron salt is used to preserve wood (Resource 10, Additional Resources). This symptom is indicative of minor exposure to these substances. Higher levels of exposure can be life-threatening (Resource 8, Additional Resources).

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