The Dangers of the Sun: Melanoma

Who doesn’t love a bit of sunshine? While the sun makes for some really pleasant days, we’ve all heard about the dangers of unprotected exposure. So what is it that makes basking in the sun without any UV-protecting sunscreen unadvisable? Skin cancer. There are two different types of skin cancers: melanoma and non-melanoma skin cancer. The two different subtypes of nonmelanoma cancer, Basal Cell Carcinoma, and Squamous Cell Carcinoma, are common and also relatively simple to treat if they are recognized at an early stage. Melanoma, on the other hand, is incredibly dangerous because it can easily spread to other parts of the body. In this article, we are going to look at the effects of sun exposure and genetics on the risk of developing melanoma.

Let’s start with the question: What is melanoma? It is characterized by new unusual growths on the body due to uncontrolled division of cells in the skin. Now, how does excess sun exposure cause melanoma? The UV light rays from the sun damage the cell’s DNA by initiating a reaction between two molecular “DNA blocks” called thymine, forming something known as a thymine dimer. This can be better understood by looking at the picture below. When DNA replicates without fixing this thymine dimer, it can cause trouble with cell division and eventually lead to cancer. However, UV rays act on different skin types in different degrees. Melanocytes are cells on the skin that produce melanin granules which give pigment to our skin (Riley 1997). Different amounts of melanin, the pigment-producing hormone, is what results in different skin colors. Interestingly, melanin protects the skin from UV rays by absorbing them, thereby making sure they don’t touch DNA. This explains why people who live near the equator are generally dark-skinned, with more melanin to help defend the skin against high sun exposure. 

In a study by Elder (1995), researchers collected skin cancer information from various databases to analyze different factors and their effects on melanoma risk. The paper observed a 13-fold difference for the incident rates between black and white people, indicating that white people are more at risk to get melanoma compared to black people. This again can be explained due to melanin, as black individuals have more melanin that can tolerate stronger light rays. There was also a significant difference in the incidence rates between males and females; melanoma was more invasive in males than in females.

Additionally, Ivry et al. (2006) compared effects of different levels of sun exposure on the development of melanoma. They observed that older white males who are exposed to sun have the steepest incidence rates for the development of melanomas. Intermittent, chronic, and cumulative sun exposure are most likely to develop into new nevi (moles) that have the potential to turn into skin cancer. Supporting the strong correlation between sun exposure and cancer, various studies have also shown that the use of sunscreen can cause a decreased rate in formation of new nevi, ultimately leading to decreased risk of skin cancer.

In addition to sun exposure, genetics plays a huge role in the development of melanoma. Studies have found evidence that people with an autoimmune genetic disease like Xeroderma pigmentosum have a 1000-fold greater risk in developing melanoma (Paszkowska-Szczur et al. 2013). This is because individuals with this disorder are unable to repair UV light-induced mistakes in DNA, like the thymine dimers, leading to an increased risk of incorrect DNA replication, and in turn, cancer. Other evidence for the role of genetics is found in studies such as by Lana, Douglas, and Sancy (2006) who found that people with a family history of melanoma are more likely to get melanoma, especially with increased UV light exposure. 

Interestingly, sun exposure is not always a bad thing. In fact, moderate amounts are beneficial because they trigger skin cells to make vitamin D. Some amount of exposure to the sun is also known to aid immune cells to toughen up against UV rays and better prepare skin for higher sun exposure. So the key is to avoid prolonged submission to the sun and to use protective sunscreen when possible. 

Now we’ll ask again, who doesn’t love a bit of sunshine? If there’s one main takeaway from this article, it’s the importance of protection against the sun’s harsh UV rays. Inculcating the use of sunscreen in our daily habits is highly beneficial. What do you think about sun exposure and skin cancer? Let us know your thoughts in the comments below!


References

Elder, David E. “Skin cancer. Melanoma and other specific nonmelanoma skin cancers.” Cancer 75.S1 (1995): 245-256

Ivry, Gil B., Christina A. Ogle, and Elisabeth K. Shim. “Role of sun exposure in melanoma.” Dermatologic surgery 32.4 (2006): 481-492.

Paszkowska‐Szczur, Katarzyna, et al. “Xeroderma pigmentosum genes and melanoma risk.” International journal of cancer 133.5 (2013): 1094-1100..

Pho, Lana, Douglas Grossman, and Sancy A. Leachman. “Melanoma genetics: a review of genetic factors and clinical phenotypes in familial melanoma.” Current opinion in oncology 18.2 (2006): 173-179.

Riley, Patrick A. “Melanin.” The international journal of biochemistry & cell biology 29.11 (1997): 1235-1239.

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