You can find part 1/2 here: https://glamsci.blog/2021/02/25/the-sun-and-skin-part-1-2-pigmentation-and-melanin/
Sunburn is common but it shouldn’t be. The effects of sunburn can be dangerous and can even lead to skin cancer. Protecting our skin from the sun is ever more important with climate change and rising exposure to the sun. It seems a nuisance to apply sunscreen on holiday but always wear it for your own comfort and health.
How does sunburn happen?
Solar erythema is another name for sunburn because it is caused by the sun and causes inflammation .
Sometimes sunburn can be confused with thermal burns as both are caused by radiation. Thermal burns are caused by infrared radiation whereas sunburn is caused by ultraviolet (UV) radiation.
There are multiple types of UV:
- UVA – penetrates deep into the skin. This causes ageing of the skin and wrinkles in the long term. UVA is commonly used in tanning beds.
- UVB – these are shorter wavelengths so will not penetrate the skin as deep. However, these are the rays that cause sunburn in the short term but in the long term can lead to cancer.
- UVC – this is blocked by the ozone layer so does not even make it to the Earth’s surface (there are some manmade sources though). But it is a very dangerous form of UV because it has the shortest wavelength and highest energy level.
UVA is in the most abundance and is the least blocked by the clouds and it can even penetrate windows. UVB can’t penetrate windows due to its shorter wavelength and is also more likely to be blocked by clouds.
Photo Credit: Vision Ease
You can see here that the UVB rays are shorter than UVA so they will not penetrate the skin as deep. The UVA also has a lower energy level so are more likely to damage DNA indirectly. UVB will have a higher energy level so will damage DNA directly.
You can also see that UV has a shorter wavelength than visible light, so we won’t be able to see UV like we can see light.
There are different types of sunburns that indicate the level of damage done to your skin. A first degree sunburn will effect only the epidermis (outermost layer of skin). A second degree burn will effect the dermis and will damage nerve endings. A second degree burn will take longer than a few days to heal.
The effects of sunburn
After a few hours of exposure to the sun you will develop a sunburn. Sunburns are usually itchy, red and can be quite painful. The pain is usually produced from your bodies own repair mechanism after the UV rays have damaged cells. Inflammation will be initiated by our body.
Mast cells are activated in the damaged tissue and they release two types of chemicals: histamines and cytokines.
- Histamines cause vasodilation (dilation of the blood vessels). This increases the heat of your skin because more blood is flowing closer to the outer layer of the skin. The histamines will also make the vessels more leaky to allow more tissue fluid and plasma to the site of burn. This means that immune cells are brought to the site. This is also characterised by swelling.
- Cytokines signal to the immune cells to kill cells that have DNA damage. If some cells are missed, this could cause a tumour to develop.
In the short term you will experience pain and swelling. After a few days, your skin will begin to peel off. This is your body getting rid of the dead skin cells after the immune response. Moisturising during this period will help to speed up the process of repair and replacement.
The short term immune response tried to get rid of all cells with damaged DNA but sometimes they might miss a few cells. Firstly lets look at what and how our DNA is damaged:
The high energy UV photons will penetrate the skin and generate free radicals. Free radicals occur when there is an unpaired electron. They damage our cells by breaking them down which in turn damages our DNA, causing ageing and cancer.
Usually the number of free radicals in our body is regulated by antioxidants that donate an electron to reduce their reactivity. As we get older there are also less antioxidants in our body and there are more free radicals. Increased exposure to free radicals will reduce the effectiveness of antioxidants and speed up the rate of ageing.
Damaged DNA is not a good thing because the DNA is the instructions for our cell. Without proper functioning DNA, a cell will not synthesise the correct proteins or enzymes for reactions and will also divide uncontrollably. Uncontrolled cell division can form a tumour.
There are multiple types of skin cancer. But these are the most talked about:
- Melanoma (melanoma is quite rare but SCC and BCC are more common non-melanoma cancers)
- Squamous Cell Carcinoma (SCC)
- Basal Cell Carcinoma (BCC)
SCC is caused by mutations (changed DNA) in the squamous cells in the epidermis layer of the skin. A particular tumour suppressor gene is damaged in the DNA which means that mutated cells can live longer. BCC (in the basal cells of the epidermis) is also caused by a mutation of a tumour suppressor gene (a different one to SCC). The effects are the same. Melanoma is caused by damaged melanocytes (the cells that produce melanin)
Obviously, getting a sun burn doesn’t mean you will age ridiculously fast or develop skin cancer. But protecting our skin should be a priority in the summer months. Cover up your skin with clothes or apply good sunscreen to prevent damage. Remember that excessive exposure to the sun is not healthy.