#912 Why does sunburned skin peel?

Why does sunburned skin peel? It peels because the skin cells are dead, and the body is getting rid of them to make way for new cells.

When looking at what makes sunburned skin peel, we have to look first at what causes sunburn? It is caused by ultraviolet light that comes from the sun. The sun is an enormous fusion engine in space. It is so hot and there is so much pressure that hydrogen elements are pressed together so hard that they overcome the repulsive electrostatic forces that keep atoms apart and are fused together. When four hydrogen atoms are fused together, they become a molecule of helium. One atom of helium has a slightly lower mass than four atoms of hydrogen and this extra mass is released as energy because mass is energy. This energy leaves the sun in a whole range of wavelengths. Some of them are very long and these are radio waves. Some of them are very short and these are gamma rays. In the middle are the visible light spectrum, which make up the colors we can see, and ultraviolet light. Ultraviolet light has shorter wavelengths than the light we can see because it has more energy.

When visible light hits our skin, some of it is absorbed and some of it is reflected, giving our various skin colors. UV light has more energy, though, and it can cause a lot of damage to our skin cells. We have a defense mechanism, which is our melanin. When we are hit by a lot of UV light, we release more melanin, which is the pigment in our skin, and we go a darker color, which can reflect more UV light. However, if the UV light is strong enough, being brown doesn’t really matter and we can burn. The UV light energy travels through our skin and strikes the cells that are there. The energy is imparted to the electrons, and that can damage the cells because these more powerful electrons can change the shape of the molecule they are orbiting around. Sunburn is caused when UV light hits the electrons around the RNA that is inside the nucleus of our skin cells, changing its shape.

Sunburn is our body’s evolved response to the UV light hitting the RNA and altering it. When the RNA’s structure is changed, messenger molecules called cytokines are released. These are the first part of the immune response. Their job is to call white blood cells to come and fix the burn. To do this, they bring more blood into the area to transport the white blood cells, and this is where the red coloring and the heat of sunburn comes from. The white blood cells are there to remove the damaged cells. There is a cytokine called CXCL5 which is the one responsible for getting the white blood cells into the area they are needed. The problem is, they are needed inside the skin’s dermis layer, and they crowd the area, pressing on pain receptors in our skin, causing the pain of sunburn.

There are different levels of sunburn, just as there are different levels of any kind of burn. They are basically divided up on how deep into the skin the burn goes. A 1^st degree burn is superficial and there are no blisters. The skin is not broken, and the burn has only reached the outer layer of skin, which is called the epidermis. Most mild sunburns fall in this category. 2^nd degree burns go through the epidermis to the top part of the next layer of skin, which is called the dermis. This is where new skin cells are made. There are a lot of blisters. Severe sunburn can do this, but you really need to be in very hot sunlight for a long time. Then there are 3^rd degree burns, which destroy the epidermis and the dermis. The function of the skin is lost, and a skin graft is usually necessary. There is a fourth degree burn, but no sunburn could reach it.

Most sunburn is a first degree burn, which is why the sunburned skin peels off in sheets. The UV light has damaged all of the cells in the epidermis layer of skin, but not the dermis layer below it. The cytokines have summoned the white blood cells, which have culled all of the dead cells. We lose skin cells all of the time. Nearly all house dust is made of dead skin cells. However, they usually flake off. New cells are formed in the dermis, below the epidermis, and when the outer cells are dead, they flake off and are replaced by new cells. With sunburn, a whole patch of skin will be dead. It won’t be attached to the dermis anymore, and it will peel off in a large patch to make way for the new cells underneath it. If the sunburn is worse, it could take longer to heal, but our bodies can heal completely from even second degree burns, which is pretty much the worst a sunburn can be. And this is what I learned today.

Image By Phil Kates – https://www.flickr.com/photos/hawk684/108139247/, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=51031248

Sources

https://www.britannica.com/science/electromagnetic-spectrum

https://energyeducation.ca/encyclopedia/Nuclear_fusion_in_the_Sun

https://science.nasa.gov/ems/10_ultravioletwaves

https://www.abc.net.au/news/science/2015-11-18/how-uv-light-damages-our-skin/6856742

https://www.mountsinai.org/health-library/symptoms/sunburn