Originally I was going to start this post talking about ultraviolet radiation but I thought maybe I would give you some background on our body's way of protecting ourselves from it first. In the bottom layer of our skin we have cells called melanocytes. These cells produce melanin and insert the melanin into melanosomes (specialized cellular vesicles). The melanosomes are then transferred into skin cells in our epidermis. Once in a skin cell melanosomes accumulate on the cell nucleus where they protect the nuclear DNA from being damaged by ultraviolet radiation (UVR). (source) Melanin protects the nuclear DNA by absorbing UVR and dissipating the energy as harmless heat. (source)
Ultraviolet radiation (UVR) is produced naturally by our sun and artificially by sources like tanning bed bulbs. There are 3 types of UVR rays: UVA, UVB and UVC.
UVC has the shortest wavelength and the most energy, but it doesn't reach the Earth's surface because it's stopped by ozone in the Earth's atmosphere.
UVB light is between UVA and UVC in wavelength and energy and is the primary cause of sunburns. UVB light can cause direct DNA damage. Direct DNA damage happens when the radiation excites DNA molecules in skin cells, causing adjacent thymine bases to bond with each other, instead of across the "ladder". This "thymine dimer" makes a bulge, and the distorted DNA molecule does not function properly. (source). When this happens either type 1 cell-death is triggered, the DNA is repaired by our body or the cell is replicated with the damaged DNA. When the damaged DNA is replicated a DNA mutation will be present in the new skin cell. This mutation can result in cancerous growths. From what I can tell these growths form the two most common types of skin cancer: squamous cell carcinoma and basal cell carcinoma. For more information on skin cancer go here.
UVA has the longest wavelength, the least energy, and the most penetrating power of the 3 types. Of all the UV light that reaches the Earth, about 95% of it is UVA. (source) Studies have shown that increased exposure to UVA rays can cause pre-mature aging of the skin and indirect DNA damage. From my understanding indirect DNA damage causes malignant melanoma (for more details go here). Melanoma is the least common type of skin cancer but it is the deadliest causing 75% of skin cancer related deaths (source).
Tomorrow's post will talk about sunscreens (what's in them, natural vs. artificial, recommendations), how they work and what to do if you find yourself looking a little red after a day outside.