1Hey, it's Danny.
2I want to show you a picture of someone very special to me.
3That's my grandma.
4This was taken on her birthday when she turned 83 years old.
5Someone named Yusra is curious about a change that happens as people get older.
6Let's give Yusra a call now.
7Hi Danny.
8Hi Yusra.
9I have a question for you.
10Why does hair turn gray?
11That's a great question.
12Humans have so many cool hair colors,
13all different shades of brown, red, black, and blonde.
14Along with all this natural variety,
15there are also colors that people dye their hair,
16like pink, green, and rainbow swirl.
17As people get older, their hair color can also change.
18Today, my grandma's hair is silvery white,
19but here's a picture of when she was younger.
20Back then, her hair was brown.
21Maybe you know someone whose hair has turned gray over time as well.
22So why is it that someone whose hair is naturally brown, or red, or black, or blonde
23can end up with hair that's gray?
24To figure this out, let's start with how hair grows.
25If you look closely at a single strand of someone's hair,
26you can follow it back to their head, right?
27Here's what that looks like up close.
28See if you can tell where the strands of hair are coming from.
29What do you notice?
30Maybe you noticed how each strand comes out of a tiny hole in the skin,
31like this one here.
32If you could look inside that tiny hole underneath the skin,
33you'd see where hair starts growing.
34Inside each hole is a little thing called a follicle.
35A follicle produces material that your hair is made out of.
36The material builds up bit by bit,
37creating the strand of hair we see.
38This part of your hair isn't alive.
39It only grows from this end.
40That's where the follicle keeps adding more material,
41which makes the strand longer.
42Then, eventually, that strand falls out,
43and the follicle starts forming a new strand in its place.
44If you're curious to know more,
45we have a lesson all about how hair grows.
46But those are the basics,
47except for one very important detail.
48You see, as each follicle makes hair material,
49your body adds a substance called melanin.
50Melanin is what gives your hair its color.
51It's what gives your skin and eyes their color too.
52Hair color comes from two main kinds of melanin:
53one that's more black-brown
54and one that's more red-yellow.
55That means from just two kinds of melanin,
56we get all of these natural hair colors.
57How amazing is that?
58All that variety comes from different amounts and combinations of the two.
59So your hair has its own particular melanin mix.
60But now, check out this person's hair that's starting to go gray.
61See how they have some strands that are dark
62and some that are lighter?
63What's going on there?
64Well, over time, when new strands form,
65less and less melanin gets added to the hair material.
66A strand with less melanin ends up looking lighter.
67That's because the material our hair is made out of is pretty much colorless,
68as in no color.
69Without melanin, a strand of hair is basically clear.
70But when light hits it, the strand ends up looking more silvery white.
71So even though we call them gray hairs or white hairs,
72we're really talking about nearly clear hairs.
73Sounds strange, but it's true.
74And when a person's hair turns gray,
75it's because they're growing more of those nearly clear hairs with less melanin.
76Scientists are still studying why less melanin gets made and added to hair material over time.
77But overall, growing gray hairs is just a normal part of getting older.
78And it's not something you have much control over.
79If your grandparents and parents got gray hairs in their 20s,
80there's a good chance you will as well.
81Or if they have dark hair into their 70s,
82that might be you someday too.
83That's because people who are related tend to get gray hairs around that same age.
84So in summary, hair has color because of a substance called melanin.
85Over time, less melanin gets added as new strands of hair form.
86Strands with less melanin look lighter
87because the material our hair is made of is pretty much clear.
88So when someone's hair looks gray or white,
89it really means they're growing more of those nearly clear strands instead of colorful ones.
90Without melanin, we'd all be rocking clear hair.
91That's all for this week's question.
92Thanks, Yusra, for asking it.