Why/How Does the Blond-Born Childrens' Hair Usually Grow Darker As They Get Older?

[Melisande]

Some of the answers here are pretty good (although broaden "hormones" to "various proteins including hormones").

Also, parse the question more narrowly. Are we talking about 1 day olds whose hair changes by age six months? Or six month olds who are still tow-heade by who are brunettes by 2?

Or (common) gradually turning from a small amount of blond hair to light brown hair by age four, then darker by age six - and so on?

Developmental genes are involved (and they do produce hormone or hormone-like molecules that affect melanin/pigmentation).

Likewise, some light brown hair (at birth) is subject to quite a bit of lightening by an older age, due to DEpigmentation processes - so that a child can be born with brown hair and end up blondish (especially if their hair is long - and by long, I mean long enough to turn blond, not any particular length of hair).

[feisty goddess]

Being blonde as a child or baby and not as an adult is a very common caucasian trait, even plenty of non-Germanics have it. Everyone is born lighter than they will be as an adult (even nonwhites), I'm not exactly sure why this is though.

[ronnyquest]

When I was young, my eyes were blue and hair was blond. I have pictures where I really, really look to be of stereotypical Norwegian descent. My beard grew in blond with some red.

However, as I grew older, my hair darkened to medium brown and my eyes became green. My beard now is darker, but still retains some of the blond of my youth (and gray of age). My dad's hair did the same as he grew older, but his brothers and sisters who started blond are still blond with blue or green eyes. We all still have fair skin. I have always wondered and asked a few people over the years who gave various kind of answers, but nothing satisfying.

[Nooitgedacht]

My hair was white up to age +/- 11. Then it became brown.

My daughter had pitch black hair up to +/- 10 and she is blond now.

[Marielise]

I was born with red/auburn hair, lost them and then they grew back honey-blond but they steadily darkened as I grew older, by age 12 they were light brown with some red. In the summer, they get paler, the little baby hair around my face are white and the rest gets honey brown...

[Jäger]

Developmental genes are involved (and they do produce hormone or hormone-like molecules that affect melanin/pigmentation).

Isn't testosterone one of the culprits here? Women (who evidently have less testosterone levels) are on average lighter than males, and elderly people (whose hormone production is decreasing) depigment usually as well.

[Goomer]

Blonde women's hair will usually darken a little after childbirth has occurred. It's one of the sociobiological reasons men tend to be attracted to blondes; as a signifier of youth, and perhaps even virginity.

[Frostbite]

My hair was dark when I was born, turned white blonde when I was a small child and got darker as I grew. Now it's a reddish brown. My eyes also went from blue to hazel/green. Strange how that works.