if our skin cells are constantly dying and being replaced by new ones, how can a bad sunburn turn into cancer YEARS down the line?
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Its not like we have an untouchable entity that manufactures our cells, making sure they’re completely identical forever. If that was the case, cancer would be impossible. What allows sun damage to cause skin cancer is the damaging of our cells’ ability to divide and replenish properly, by going into overdrive. It isn’t that replacing our skin should make us immune to cancer, it’s the very mechanism that allows that replacement that makes us vulnerable to cancer in the first place.
**ELI5:**
Cancer is like a box of pencils. Imagine you have a big box of pencils, that needs to last you until high school.
Losing pencils is bad, because it means you won’t be able to do your homework. It’s especially bad if you lose a lot of them. Imagine if you tripped and broke half of your pencils. That sucks, but it’s okay since you have a pretty big box of pencils, and there’s still a lot in there. You finish 3rd grade with plenty of pencils left.
Over the years, you lose one here or there. You successfully finish some of them, and proudly show off the tiny eraser, telling your mom you worked hard.
By the end of 6th grade, you don’t have that many pencils left. Eventually, you use up the last pencil, and the underpaid teacher can’t afford to buy you a new box of pencils. You don’t get to go to high school because you can’t do your homework. The end. Take care of those pencils, you’ve got a lot of years of school, and they need to last a long time.
**ELI20:**
The body has many mechanisms to prevent cancer, sort of like fail-safes in case any number of them are damaged.
To simplify, let’s just say there’s only two mechanisms: die if DNA is damaged, and grow only when told to.
It’s very unlikely for any one cell, by random chance, to have damage to both of these protective mechanisms.
If you get a bad sunburn, you might damage the first mechanism. So the damaged cell no longer kills itself when it notices excessive DNA damage. Still, it doesn’t grow abnormally, so it’s not cancer, and overall you’re fine.
Most of these cells are pushed out and die off, but the radiation penetrated deep enough to affect the stem cells that are responsible for replenishing the skin layers. The stem cells are never replaced, so the damage sticks around for the rest of your life. All of the offspring of that stem cell will have damage to the first mechanism.
Decades later, it just so happens that UV radiation hits one of the offspring of that damaged stem cell in just the right spot, causing it to grow even when it hasn’t been told to. Now you’ve lost both protection mechanisms, and you have cancer.
If it was any other cell, it would have been fine, because the first protective mechanism would have killed off the damaged cell, preventing the cancer. But because you had a bad sunburn in the past, you’re at a much high risk of cancer in the future. Wear your sunscreen. You only have so many pencils in your box.
Correct me on this…Maybe skin cancer affects the inner dermis cells (which give rise to all the skin layers above) and not the ephemeral surface epithelium?
Skin has layers. The outer layers are the ones known for constantly dying and being replaced, but there’s a layer beneath that which is what feeds most of the replacing.
Most of the really bad damage with sunburns only gets those outermost layers, but a really bad one can get the really bad damage all the way down to the layer which does the replacing. That damage is what leads to cancer years later as those cells do their normal replacement among each other
Light is made of little particles called photons. They have energy. UV light that gives a sunburn has more energy than the light you can see. UV light has so much energy that when it hits your skin, it pushes the cell that it hits further into your skin. (This is why sun burn hurts.) As we know, your skin grows from the inside out and the longer the UV-impacted cell stays deep in the skin layer, the more the cell can grow and divide. But also, the pressure is higher within the skin the deeper you go.
So, what happens when you get sunburn is that a whole bunch of cells get pushed deep into the skin layer by the UV light particles. Some of them might get pushed so deep that it takes years for them to grow back out to the surface. That gives the cell plenty of time to grow. But, because the cell is now so deep in the skin, the pressure surrounding the cell prevents cell division. So the cell grows extra large: 5-100 times the size of a healthy skin cell. So when the large, now-cancerous, cell reaches the surface, it starts dividing into similarly large and malformed cells creating the cancer.
>ELI5 if our skin cells are constantly dying and being replaced by new ones
Cells not dying when they should is literally cancer.
Think of sunlight photons as shotgun pellets. Most of the human body is free space on an atomic level. But when a light photon traveling at the speed of light interacts with an atom that makes up part of the string of DNA it can alter the way that DNA reproduces all the cells afterwards. Some damage does nothing noticable. Other damage killed both my parents.
Not all cells die, the new ones don’t appear out of thin air.
The skin cells of the superficial layer (Epidermis) of the skin – which is divided into four or five sublayers – is formed at the bottom layer, as cells there divide. Some of these cells migrate to become more superficial (and then later on die), while some, “immortal cells” (also called stem cells), in the deepest layer stay there to divide and produce more cells.
If the cells which divide to form new cells are damaged, then this damage will be in every cell born when they divide.
Once you have one cancer cell, it will take a very long time (up to years) until you actually can detect the cancer. The growth is exponential, which means it will be fast later on, but it also means the growth can be really slow in the beginning.
Also, damages accumulate and add up over time. Some damage can be a prerequisite for cancer. Simplified, once you get type A damage, this will not cause cancer. Neither will damage B, which is different from A. But once you get damage types A and B in the same cell, you will get a cancer cell.
Cells can also damage in a way that the cells don’t die, despite they would have been meant to be programmed to die. So, despite a cell which is not supposed to be “immortal” (or a stem cell) can start acting like one. This is bad and will result in cancer.
Let’s pretend skin cells are like tissue paper. Top layer gets dirty and used, then tossed. Imagine someone smearing poop all the way down to the bottom layer of tissue stack. Now whenever you pull out another tissue, it’s covered in poop.
UV penetrate deep into the skin damaging even skin cells that’s yet to be turned into top layer of your skin. Since cells replicate, any genetic damage not fixed will get replicated too. Even though you shed skin layers, all you get on the bottom are more bad skin like the poop smeared tissues
I ave a similar question!
I was stung my a jellyfish and a spiny caterpillar about 3 week ago.
The area on my arm STILL starts itching sometimes, and has things looking like mosquito-bites.
How can that be, 3 weeks after the fact?
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