Can sunscreen cause cancer?

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Over the decades, the sunscreen industry has seen a rise in the number of sales and are predicted to experience a growth in the coming years, of up to US$24.9 Billion by 2024. This increase is proportional to the escalation in skin cancer cases, roughly doubling every ten years. For example, in Britain in 1935, the probability of someone having the most dangerous form of skin cancer was 1 in 1500, whereas in 2000, the chance was 1 in 75. In short, as the number of people who use sunscreen increases, the more they are treated for skin cancer which raises the questions, how effective are these suncare products and do they contribute to the rise in global skin cancer cases?

Sunburns and damage to the epidermis layer of the skin is caused by excessive exposure to UV-B rays (shorter UV rays), as the longer UV-A rays can penetrate deeper into the thickest layer of one’s skin which can lead to more permanent damage. There are two types of sunscreens mainly used in the sun care market. Physical sunscreen involves blocking and reflecting ultraviolet rays from the sun, including the minerals zinc oxide and titanium dioxide. On the other hand, chemical sunscreen absorbs the sun’s ultraviolet rays of UV-A, including avobenzone, octisalate, aminobenzoic acid, oxybenzone, and octocrylene. This enables melanin production to occur in the skin yet simultaneously allows protection of the skin against sunburn. 

A study in the mid-1990s found out that fair-skinned people who had used sunscreens which contained the chemical psoralen (C11H6O3) were ‘four times more likely to develop malignant melanomas’ than people who had not used the lotion. People used in this study originated from Belgium, France, and Germany as these were the countries where high concentrations of the chemical were permitted. Consequently, the European Union committee decided via a voting system to reduce the amount of psoralen in cosmetics to one part per million. Malignant melanoma is very dangerous if not detected in its early stage because it has a high ability to spread to other organs in the body at a high rate. Although there is a correlation between the use of psoralen-containing sun creams and the chance of having skin cancer, it hadn’t been proven that the chemical was a trigger for it; psoralen may simply just not prevent the formation of malignant melanomas.

Another chemical in sun lotions which is suspected to have an effect on the increase in cases of skin cancer is Padimate-O. This is a water-insoluble organic compound linked to 4-aminobenzoic acid which is used in sun creams and is formed by condensing 2-ethylhexanol (C8H13O) with dimethylaminobenzoic acid ((CH3)2NC6H4CO2H). In sunlight, Padimate-O can generate free radicals that attack the DNA of the body, thus easily developing mutations that ultimately lead to skin cancer. It was found to be toxic to the testes, epidermis, spleen, and liver and experimentally (using human keratinocytes) shown to inhibit cell growth and DNA synthesis at low concentrations, and stopped the cell cycles of melanoma cells. Again with the psoralen, it is difficult to prove that the use of the chemical Padimate-O in sun creams provides an explanation of the pattern of risk to skin cancer. 

Oxybenzone is one of the main chemicals contained in sunscreen, absorbing both UV-A and UV-B rays and protecting the skin from sun damage. However, there has been research which can suggest that at specific exposure levels, it can be a cause of breast cancer. In January 2020, a study was published in ‘Environmental Health Perspectives’ showing that oxybenzone had damaged DNA in breast cells of mice specifically with oestrogen receptors at very low doses. Oxybenzone is considered to be an endocrine disruptor, in particular, a xenoestrogren as it mimics the female sex hormone oestrogen, affecting the body’s hormonal balance. Oestrogen is capable of causing the development and metastasis of hormone-receptor-positive breast cancer, and with this knowledge, some women have chosen to avoid using sunscreens with this chemical. However, it is important to note that there has been no conclusive evidence that oxybenzone is harmful to the human body. Additionally, scientists advise those who avoid these oxybenzone-containing sunscreens to be aware that the chemical is present in many other quotidian products as it can be encountered in plastic, hairspray and nail varnish.

The overall question is a prime example of the common phrase in statistical mathematics ‘correlation does not imply causation’. This statement in this particular situation refers to the inability to show a cause-and-effect relationship between the increase in sales of sunscreen products and the increase in cases of cancer solely on the basis of the correlation seen between them. It cannot be deduced definitely that the chemicals in sunscreen contribute to the development of cancers in the body without implicit research conducted. Studies throughout the decades have proven that chemicals in sunscreen can reduce the chances of certain skin cancers such as squamous cell carcinoma, basal cell carcinoma, and melanoma. Therefore scientists continue to advise people to use sun cream for protection against the Sun’s harmful rays, along with wearing sun-protective clothing and avoiding sun exposure when possible.


References

  1. ‘Fragile Science: The reality behind the headlines’ Robin Baker, 2001
  2. ‘Risk Assessment of Ethylhexyl Dimethyl PABA in Cosmetics’, 2019
  3. ‘Exposure to Chemicals in Sunscreen’ Breastcancer.org, September 2020
  4. ‘Is Your Sunscreen Causing Breast Cancer?’ HealthyWomen, May 2020
  5. ‘The science of sunscreen’ Havard Health Publishing, July 2018

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