And everybody has at least a few cells in them that would be called cancer if they were found. Your immune system does fight cancer, but with limited effectiveness. Once the cancer cells hijack a blood supply and get some nutrients, they can quickly replicate faster than the immune system can do anything about it (the growth rate is dependent upon cancer type, and some cancers are better at hiding from the immune system than others). In agreement with the title, the best policy is to avoid risk factors. Also, sunscreen does not block all UV, and is usually much less effective against UVA, so you cannot really rely on it for protection (but it is better than nothing).
However, UVA in itself isn't bad -it helps your skin synthesise vitamin D, and is what gives you a tan. It's UVB and UVC that you have to watch out for; they burn leaves, cause eye cataracts, and destroy DNA, which as you know, results in cancers.
I think UVC is short enough wavelength that the atmosphere, particularly the ozone layer, absorbs essentially all of it, making the amount of radiation that reaches the Earth's surface negligible for anything but a very sensitive measuring instrument. I know UVA is lower energy than UVB, but it does penetrate deeper, so is more likely to go through all of the layers of skin and reach the live cells. This can cause basal cell carcinoma or malignant melanoma. The long term exposure, deeper penetration, and usual lack of protection (you have to make sure your sunscreen says specifically that it blocks both UVA and UVB, otherwise it just does UVB) is why UVA is dangerous.
You are not technically permanently sunburned. You do have higher baseline levels of melanin than Caucasians , but you can still get sunburned. Sunburn involves more than just melanin, such as inflammation and epithelial vasodilation (which is why there is reddening and swelling). Black people are still alive, thus are not walking dead.
I assure you that I am quite calm. Just trying to make sure that people do not get misinformation after the usage of "technically". And this post is more like the "science side of tumblr"... but on FS.
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