July 28, 2025 • 10 mins
When our skin deepens in color after sun exposure, it's trying to protect us from damage. Learn how it works -- plus why you should help it out with sunscreen, and why some people burn instead -- in this episode of BrainStuff, based on this article: https://health.howstuffworks.com/skin-care/beauty/sun-care/sunscreen.htm
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Episode Transcript
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Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff,
Lauren vogelbaumb here. The warm sun can feel so good
on your skin, and getting a bit of color from
it can be beautiful. But we all know it's important
to protect ourselves from the damage that the sun can do.
Our planet does a fairly good job of protecting us.
(00:25):
You might remember from our Sunburns in Space episode that
Earth's ozone layer absorbs nearly all of the damaging ultraviolet
light that the sun puts off. Sunscreen, sunglasses, and appropriate
clothing can help us defend against the UV light that
does get through. But today let's talk about our first
line of defense, our skin. Skin is one of the
(00:47):
most amazing organs of the human body. It's weird to
think of it as an organ because we tend to
think of organs as these sort of boxy things. Your heart, liver, kidneys,
those are obviously organs. But an organ, by definition, is
a structure made up of cells and tissues that performs
or helps perform some function in our body, which definitely
(01:09):
applies to skin. Skin is made up of very specific
cells and tissues, and their collective purpose is to act
as the boundary between you and the world. Most of
our organs don't directly interface with the world around us,
but the skin does, which is why it's loaded with
sensors and has a very tough layered design so that
(01:31):
it can handle things like abrasion and sunlight. Our skin
is made up of three main layers, the epidermis on
the outside, the dermis in the middle, and the hypodermis
on the inside. The epidermis is the barrier. The dermis
contains all of the equipment, things like nerve endings, sweat glands,
hair follicles, and so on, and the hypodermis provides structural support,
(01:54):
also called the subcutaneous layer. The hypodermis contains fat to
insulate and protect are underlying muscles and organs, plus blood
vessels to supply the equipment in the dermis. But today
let's focus in on the epidermis. The epidermis itself has
two main layers, the inner of which is living and
the outer of which is dead. The dead skin cells
(02:17):
of the outer layer are what we see and touch,
and it's called the stratium corneum. The cells in this
layer are filled with a protein called keratin. Keratin is
interesting because it's tough. Horns, hair, hoofs, fingernails, and feathers
all gain their strength from keratin. Yes, the same stuff
that your fingernails are made of actually forms your visible skin,
(02:39):
but in a much thinner and more flexible layer. That
is what makes your skin so tough. In parts of
the body that get a lot of wear, like the
palms of the hands and soles of the feet, the
stratium cornium is thicker to handle the abrasion. The cells
of this layer are constantly flaking off and being replaced
by newer, dead skins being pushed outward. Those cells are
(03:03):
created in the living inner layer of the epidermis, which
is called the malpigean layer. It sidles up to the dermis,
which feeds and supports it, and this is where the
sun affects our skin When we ten. The innermost part
of the malpagean layer, called the basal layer, is where
we produce those new tough outer skin cells, and also
where we produce melanin. Melanins are a group of pigments
(03:27):
found in several places in our bodies, but most relevant
today in our eyes, skin, and hair. The two main
types of melanin found there are eumelanin, which can be
brown to black in color, and fiamelanin, which can be
yellow to red. They're produced by cells called melanocytes, and
no matter what color your skin is, it contains about
(03:49):
one thy two hundred melanocytes per square millimeter, which is
four hundreds of an inch, which is really small, which
means that we have a lot of melanocytes. Our skin
color is determined by how much and what types of
melanin those cells produce. So okay, when your skin tans
or deepens in color, what's happening is that your melanocytes
(04:12):
are producing eumelanin pigment in reaction to the ultraviolet light.
In sunlight, ev light can damage our cells, and our
bodies evolved the ability to mitigate that with eumelanin. Eumelanin
absorbs ultraviolet light and thus protects our cells from damage.
So our bodies developed this technique that when we're exposed
(04:32):
to UV light that stimulates the production of melanin. A
melanin production takes a fair amount of time. That's why
most people can't get a ten in a single day.
First you have to expose yourself to UV light for
a short period of time to activate the melanocytes. They
produce melanin over the course of a few hours, and
by repeating this process over five to seven days, pigment
(04:55):
builds up in your cells to a level that's more
protective than your baseline. Of course, people's baseline of melanin
can vary wildly. People with darker skin are lucky to
have elevated protection from UV radiation all the time. That
doesn't mean you shouldn't wear sun protection though. Also your
balance of types of melanin matters. Again. Eumelanin is what
(05:19):
creates a tan, so people whose skin produces more feomelanin
and less eumelanin, like many light skinned redheads, don't tan
very well. This is caused by variations in a particular gene,
the MC one R gene, to be specific. This gene
also controls whether you freckle. Freckles are spots of hyperpigmentation
where for some reason, your skin clusters production of eumelanin
(05:42):
instead of spreading it out. People with albinism have no
melanin in their skin, hair, or eyes. The chemical pathway
that produces melanin can't proceed because an enzyme called tyrosinase
is missing. But no matter what your skin color or
whether it deepens with sun exposure, getting too much sun
can cause damage to your skin. In the short term,
(06:04):
too much sun can cause a sunburn, leaving your skin
red and painfully tender, and sometimes even blistered. When you
get a sunburn, what you're really getting is cellular damage
from ultraviolet light. The body responds to the damage with
increased blood flow to the capillary bed of the dermis
in order to bring in cells to repair that damage.
(06:24):
The extra blood in the capillaries is what causes redness.
That's why if you press on sunburned skin, that will
turn white and then return to red as the capillaries refill.
In the long term, uv light can break down elastin
fibers in your skin, which help give skin its bouncy structure.
The cells throughout your skin's layers can be damaged too,
(06:45):
of forcing them to repair themselves over time. This stress
can affect the cell's DNA, which makes them less able
to produce new cells and function properly. All of this
can cause visible signs of aging, like wrinkles in sunspots,
but more importantly can cause pancers like melanoma or basal
cell carcinoma, but which start with damage in the melanocytes
(07:06):
and those basal layer cells, respectively. All of this is
why it's really good to wear protection when you're going
to be outside during daylight hours, especially if it's sunny.
But even if it's cloudy, BEUV light is still there. Hats, sunglasses,
and long sleeves and pants or skirts can all help
block it. But let's talk about the layer you put
on first. Sunscreen sunscreens are designed to either physically block
(07:31):
or chemically absorb UV light before it can reach your skin.
Creams that go on white are usually physical blockers. That
white tint is from fine particles of minerals like a
titanium dioxide or zinc oxide, that reflect UV light. They
can look a little chalky on your skin, but they
usually don't cause any irritation. Chemical sunscreens absorb UV light
(07:53):
and in doing so, emit a very low level of heat.
Usually it's too low to notice, but these sunscreens are
more lightly to cause irritation or an allergic reaction. Some
formulas contain both physical and chemical elements. Look for broad
spectrum sunscreens that means that they block a wider range
of types of ultraviolet light, and look for waterproof or
(08:15):
sport formulas. Find one that's SPF thirty or higher. SPF
stands for sun protection factor, and the number refers to
how much UV light the product blocks SPF ten, For example,
let's one tenth of UV light through or ten percent
SPF thirty only, let's one thirtieth of UV light through
(08:35):
or three percent. After that, you get diminishing returns because
of how fractions work. It can be worth it, though,
if your skin is light and you don't tan in
any case, you want to apply sunscreen generously about half
an hour before you'll be outside to give it time
to settle into your skin. Reap every couple hours or
more often if you think that you might have swam
(08:57):
or sweat or toweled your initial application off. Interestingly, in
people who do tan, the stimulation of melanin production can
happen when UV light hits your skin or your eyes.
Melanocytes are prompted to produce more melanin when they receive
a hormone called appropriately melanocyte stimulating hormone. This hormone can
(09:19):
be produced locally by skin cells that are exposed to
UV light, but it's also produced by the pituitary gland,
where many of our hormones are produced. The pituitary gland
is tied into the optic nerve, which means that it
responds to light that comes in through your eyes. So
when you wear sunglasses in bright sunlight and block some
of that UV light from hitting your eyes, your petuitary
(09:41):
gland produces less of the melanocyte stimulating hormone and you
won't tan as much, which is why a sun blocking
system of eye protection, appropriate clothing and sunscreen is the
best way to prevent sun damage. Today's episode is based
on the article how Sunburns and suntan's work on HowStuffWorks
(10:04):
dot Com, written by Marshall Brain Brain Stuff is production
by Heart Radio in partnership with HowStuffWorks dot Com and
is produced by Tyler Klang. For more podcasts my heart Radio,
visit the iHeartRadio app, Apple Podcasts, or wherever you listen
to your favorite shows.
Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff,
Lauren vogelbaumb here. The warm sun can feel so good
on your skin, and getting a bit of color from
it can be beautiful. But we all know it's important
to protect ourselves from the damage that the sun can do.
Our planet does a fairly good job of protecting us.
(00:25):
You might remember from our Sunburns in Space episode that
Earth's ozone layer absorbs nearly all of the damaging ultraviolet
light that the sun puts off. Sunscreen, sunglasses, and appropriate
clothing can help us defend against the UV light that
does get through. But today let's talk about our first
line of defense, our skin. Skin is one of the
(00:47):
most amazing organs of the human body. It's weird to
think of it as an organ because we tend to
think of organs as these sort of boxy things. Your heart, liver, kidneys,
those are obviously organs. But an organ, by definition, is
a structure made up of cells and tissues that performs
or helps perform some function in our body, which definitely
(01:09):
applies to skin. Skin is made up of very specific
cells and tissues, and their collective purpose is to act
as the boundary between you and the world. Most of
our organs don't directly interface with the world around us,
but the skin does, which is why it's loaded with
sensors and has a very tough layered design so that
(01:31):
it can handle things like abrasion and sunlight. Our skin
is made up of three main layers, the epidermis on
the outside, the dermis in the middle, and the hypodermis
on the inside. The epidermis is the barrier. The dermis
contains all of the equipment, things like nerve endings, sweat glands,
hair follicles, and so on, and the hypodermis provides structural support,
(01:54):
also called the subcutaneous layer. The hypodermis contains fat to
insulate and protect are underlying muscles and organs, plus blood
vessels to supply the equipment in the dermis. But today
let's focus in on the epidermis. The epidermis itself has
two main layers, the inner of which is living and
the outer of which is dead. The dead skin cells
(02:17):
of the outer layer are what we see and touch,
and it's called the stratium corneum. The cells in this
layer are filled with a protein called keratin. Keratin is
interesting because it's tough. Horns, hair, hoofs, fingernails, and feathers
all gain their strength from keratin. Yes, the same stuff
that your fingernails are made of actually forms your visible skin,
(02:39):
but in a much thinner and more flexible layer. That
is what makes your skin so tough. In parts of
the body that get a lot of wear, like the
palms of the hands and soles of the feet, the
stratium cornium is thicker to handle the abrasion. The cells
of this layer are constantly flaking off and being replaced
by newer, dead skins being pushed outward. Those cells are
(03:03):
created in the living inner layer of the epidermis, which
is called the malpigean layer. It sidles up to the dermis,
which feeds and supports it, and this is where the
sun affects our skin When we ten. The innermost part
of the malpagean layer, called the basal layer, is where
we produce those new tough outer skin cells, and also
where we produce melanin. Melanins are a group of pigments
(03:27):
found in several places in our bodies, but most relevant
today in our eyes, skin, and hair. The two main
types of melanin found there are eumelanin, which can be
brown to black in color, and fiamelanin, which can be
yellow to red. They're produced by cells called melanocytes, and
no matter what color your skin is, it contains about
(03:49):
one thy two hundred melanocytes per square millimeter, which is
four hundreds of an inch, which is really small, which
means that we have a lot of melanocytes. Our skin
color is determined by how much and what types of
melanin those cells produce. So okay, when your skin tans
or deepens in color, what's happening is that your melanocytes
(04:12):
are producing eumelanin pigment in reaction to the ultraviolet light.
In sunlight, ev light can damage our cells, and our
bodies evolved the ability to mitigate that with eumelanin. Eumelanin
absorbs ultraviolet light and thus protects our cells from damage.
So our bodies developed this technique that when we're exposed
(04:32):
to UV light that stimulates the production of melanin. A
melanin production takes a fair amount of time. That's why
most people can't get a ten in a single day.
First you have to expose yourself to UV light for
a short period of time to activate the melanocytes. They
produce melanin over the course of a few hours, and
by repeating this process over five to seven days, pigment
(04:55):
builds up in your cells to a level that's more
protective than your baseline. Of course, people's baseline of melanin
can vary wildly. People with darker skin are lucky to
have elevated protection from UV radiation all the time. That
doesn't mean you shouldn't wear sun protection though. Also your
balance of types of melanin matters. Again. Eumelanin is what
(05:19):
creates a tan, so people whose skin produces more feomelanin
and less eumelanin, like many light skinned redheads, don't tan
very well. This is caused by variations in a particular gene,
the MC one R gene, to be specific. This gene
also controls whether you freckle. Freckles are spots of hyperpigmentation
where for some reason, your skin clusters production of eumelanin
(05:42):
instead of spreading it out. People with albinism have no
melanin in their skin, hair, or eyes. The chemical pathway
that produces melanin can't proceed because an enzyme called tyrosinase
is missing. But no matter what your skin color or
whether it deepens with sun exposure, getting too much sun
can cause damage to your skin. In the short term,
(06:04):
too much sun can cause a sunburn, leaving your skin
red and painfully tender, and sometimes even blistered. When you
get a sunburn, what you're really getting is cellular damage
from ultraviolet light. The body responds to the damage with
increased blood flow to the capillary bed of the dermis
in order to bring in cells to repair that damage.
(06:24):
The extra blood in the capillaries is what causes redness.
That's why if you press on sunburned skin, that will
turn white and then return to red as the capillaries refill.
In the long term, uv light can break down elastin
fibers in your skin, which help give skin its bouncy structure.
The cells throughout your skin's layers can be damaged too,
(06:45):
of forcing them to repair themselves over time. This stress
can affect the cell's DNA, which makes them less able
to produce new cells and function properly. All of this
can cause visible signs of aging, like wrinkles in sunspots,
but more importantly can cause pancers like melanoma or basal
cell carcinoma, but which start with damage in the melanocytes
(07:06):
and those basal layer cells, respectively. All of this is
why it's really good to wear protection when you're going
to be outside during daylight hours, especially if it's sunny.
But even if it's cloudy, BEUV light is still there. Hats, sunglasses,
and long sleeves and pants or skirts can all help
block it. But let's talk about the layer you put
on first. Sunscreen sunscreens are designed to either physically block
(07:31):
or chemically absorb UV light before it can reach your skin.
Creams that go on white are usually physical blockers. That
white tint is from fine particles of minerals like a
titanium dioxide or zinc oxide, that reflect UV light. They
can look a little chalky on your skin, but they
usually don't cause any irritation. Chemical sunscreens absorb UV light
(07:53):
and in doing so, emit a very low level of heat.
Usually it's too low to notice, but these sunscreens are
more lightly to cause irritation or an allergic reaction. Some
formulas contain both physical and chemical elements. Look for broad
spectrum sunscreens that means that they block a wider range
of types of ultraviolet light, and look for waterproof or
(08:15):
sport formulas. Find one that's SPF thirty or higher. SPF
stands for sun protection factor, and the number refers to
how much UV light the product blocks SPF ten, For example,
let's one tenth of UV light through or ten percent
SPF thirty only, let's one thirtieth of UV light through
(08:35):
or three percent. After that, you get diminishing returns because
of how fractions work. It can be worth it, though,
if your skin is light and you don't tan in
any case, you want to apply sunscreen generously about half
an hour before you'll be outside to give it time
to settle into your skin. Reap every couple hours or
more often if you think that you might have swam
(08:57):
or sweat or toweled your initial application off. Interestingly, in
people who do tan, the stimulation of melanin production can
happen when UV light hits your skin or your eyes.
Melanocytes are prompted to produce more melanin when they receive
a hormone called appropriately melanocyte stimulating hormone. This hormone can
(09:19):
be produced locally by skin cells that are exposed to
UV light, but it's also produced by the pituitary gland,
where many of our hormones are produced. The pituitary gland
is tied into the optic nerve, which means that it
responds to light that comes in through your eyes. So
when you wear sunglasses in bright sunlight and block some
of that UV light from hitting your eyes, your petuitary
(09:41):
gland produces less of the melanocyte stimulating hormone and you
won't tan as much, which is why a sun blocking
system of eye protection, appropriate clothing and sunscreen is the
best way to prevent sun damage. Today's episode is based
on the article how Sunburns and suntan's work on HowStuffWorks
(10:04):
dot Com, written by Marshall Brain Brain Stuff is production
by Heart Radio in partnership with HowStuffWorks dot Com and
is produced by Tyler Klang. For more podcasts my heart Radio,
visit the iHeartRadio app, Apple Podcasts, or wherever you listen
to your favorite shows.
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