Why does hair darken with age?

It’s very common to have blonde curls as a baby or a toddler, and as you get older, your natural hair colour is now a far darker brown or black. It also becomes coarser with age. Why does this happen?

It’s all down to the fact that there are several different chemicals in our body that are responsible for our hair colour. They are all within a category of compounds called “melanins”.

The predominant melanins responsible for hair colour are:

  • Eumelanin, of which there are two types:
    - black eumelanin: giving black hair
    - brown eumelanin: giving dark hair, usually brunette
  • Pheomelanin: giving red hair

People usually have a mix of these pigments in their hair, although usually one is the dominant one.

Black eumelanin and pheomelanin are usually expressed fully from birth, which explains babies born with black or red hair. Babies born with blonde hair have little, if any black eumelanin. Blonde babies could however have brown eumelanin.

People with genes that code predominantly for brown eumelanin are the ones whose hair is most likely to darken with age. This is because although they have the genes coding for brown eumelanin production from birth, these genes are not expressed to their full potential in early life.

This means that a baby could be born a blonde or a redhead (depending on the amount of pheomelanin), but with age, brown eumelanin starts to be expressed, darkening the hair. Increasing expression of pigment is linked to increasing coarseness of hair. It is a fact that blondes have softer hair than brunettes.

A 1975 study by Matheny & Dolan suggested that *when* hair begins to darken may vary between people, depending on their genetics.

The onset of brown eumelanin expression may be linked to the increased production of hormones towards puberty. Whilst it is hypothesized that there is a strong link between hair colour darkening and hormone levels, I have not yet found the answer explaining exactly how this works in my research.

As to why brown eumelanin isn’t expressed from birth, I hypothesize that it may have been advantageous for babies to stand out from adults in some visual way, to make it easier to keep them in sight at an age when they need a lot of supervision.

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11 Responses to Why does hair darken with age?

  1. Ayesha says:

    Very good article, cheers.

  2. Guy says:

    VERY interesting!

  3. sona mason says:

    thank you! the most informative response to this puzzling question I’ve found so far

  4. Susan says:

    Very well explained. Thx

  5. Tommy says:

    This is a question that always puzzled me, the same thing happened to myself. My hair was, for most of my young life, very blond, and slowly became a light brown. Certainly the most informative answer I’ve found as to why that is, thanks.

  6. Kathryn says:

    This was interesting and well explained! Thank you for writing it.

  7. Zane Bishop-Fennessy says:

    Yeah it is very odd and intriguing. I am 15 currently and my hair is auburn but it has a lot of dark brown and black but when the sun shines on my hair it goes redder for a little while. My hair as a toddler was strawberry blonde (Blonde and Ginger) but has gradually darkened over the years.

  8. Emma says:

    Really interesting to read this. I was born with black hair which quickly turned to bright red hair. My hair slowly turned darker and more auburn and my skin would tan a light golden colour. Now I’m 24 and my hair is almost fully brown (will be so sad if I can’t call myself a redhead anymore!) and my skin has changed too – now it tans a reddish brown colour. I am almost certain it is a hormonal cause as I’ve been on the pill. Finding articles like this is helpful in my research!

  9. Lynda Parker says:

    I am 71 and at the age when most people’s hair is gray or turning gray…every year my hair has become darker…now it is almost chestnut…I was born with tope almost white hair…can somebody give me an explanation of why this is happening…

    • Greg Tyson says:

      I am 67 and my previously brown hair which became a mixturevof gray and white is becoming a mixture of dark broen and gray. I too had white hair as a toddler !!I think this may be a hereditary thing ad my 70 year old sister’s hair is doing the same – as did our mother. Some of the males had dark hair until 80′s ! The rest had male pattern baldness. Seems to be on the female side. Regards

  10. Angel says:

    I remember when I was a kid, my hair is straight and a bit of light brown color, but when I get older my hair becomes curly, and turns to dark brown. Your post clearly explained what’s happening to me. thanks

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