What Causes Skin Cancer?

Cancer occurs when there is an uncontrollable and rapid spread of abnormal cells. Skin cancer is classified as cancer that starts in the skin.

Skin cancer is one of the most common cancer types in the U.S. While some individuals can be at a higher risk than others, anyone can get skin cancer.

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External causes

Cancer is caused by mutations within our genes that lead to the uncontrolled growth of cells. Skin cancer can be the result of external causes that create mutations, or less commonly, inheriting faulty genes.

While the specific factors that influence developing skin cancer vary individually, ultraviolet (UV) light from sun exposure and indoor tanning can significantly increase the risk.

Exposure to UV light

A significant risk factor for the development of skin cancer is prolonged exposure to ultraviolet (UV) light¹. The sun produces natural energy, and UV radiation is part of this, with shorter wavelengths than visible light on the electromagnetic spectrum. While your eyes can’t see UV light, your skin can feel it.

Skin cancer and tanning beds are closely linked, as tanning beds also emit UV radiation, and UV light for nails is a common risk factor to keep in mind for those who regularly visit nail salons.

Most non-melanoma skin cancers and most melanomas are associated with strong exposure to the sun’s UV radiation. When the skin is exposed to UV radiation, this creates a powerful attack on the skin, creating damage that ranges from wrinkles to dangerous skin cancers.

UV damage from sun exposure is cumulative and can increase your skin cancer risk over time. While your body can repair some DNA damage in skin cells, it can’t fix it all. Over time, the unrepaired damage builds and triggers mutations² that cause abnormal cells to multiply rapidly. That can lead to malignant tumors.

The degree of damage depends on UV ray intensity and the length of time your skin has been exposed without protection.

Two types of UV light have been proven to contribute to the risk for skin cancer. Ultraviolet A (UVA) has a longer wavelength and is associated with skin aging and wrinkles. Ultraviolet B (UVB) has a slightly shorter wavelength than UVA and is associated with skin burning.

While UVA and UVB rays have different effects³ on us, they both harm our skin. When there’s unprotected exposure to UVA and UVB, this damages the DNA in skin cells. This can cause genetic defects or mutations that can lead to skin cancer and premature aging. These rays can also cause eyelid skin cancers.

There is evidence that UV exposure that leads to sunburn plays an essential role in developing melanoma, which has been acknowledged as the most dangerous of the three most common types of skin cancer. Research has shown that the UV rays that cause skin damage can also alter a gene responsible for suppressing tumors⁴, raising the risk of sun-damaged skin cells developing into skin cancer.

Risk factors

Even if you limit your UV light exposure, you may have several risk factors that will influence your risk of skin cancer. These include your natural skin pigmentation, geographical location, the prevalence of moles on your skin, and genetics.

Skin pigmentation

Your skin type is a significant factor in your risk for skin cancer, including melanoma. People with fair skin tones are more at risk for sunburn, sun damage, and skin cancer. Even if you tan and don’t burn, UV exposure can raise your risk of skin cancer.

For all skin types, UV radiation from the sun and other sources can cause dangerous, lasting damage to your skin. This means that people from all ethnic backgrounds can still get skin cancer, even those who always tan or rarely burn.

The Fitzpatrick skin typing⁵ is a scientific skin classification system that explains six skin types, which range from very fair (type one) to very dark (type six). It was developed in 1975 by a Harvard Medical School physician named Thomas Fitzpatrick.

Skin type is classified according to the amount of skin pigment and the skin’s reaction to sun exposure. Knowing your specific skin type can help predict your overall risk for sun damage and skin cancer.

Generally, Caucasian populations have a much higher risk⁶ of getting non-melanoma or melanoma skin cancers compared to dark-skinned populations. This is due to their relative lack of skin pigmentation. Brown- and black-skinned people usually can safely tolerate relatively high levels of sun exposure without getting sunburnt or significantly increasing their risk of developing skin cancer.

Individuals with pale or freckled skin, fair or red hair, and blue or green eyes belong to the highest risk group, and people with dark hair and eyes who do not usually get sunburnt have a medium risk of developing skin cancer.

However, excessive exposure to intense sunlight can damage all skin types, and the risk of heatstroke and eye damage is also the same for everyone.

Geographical location

High and intermittent exposure to solar UV radiation appears to be a significant risk factor for developing malignant melanoma. Your location⁷ is also a factor. If you live in a country where there’s a lot of sun all year round, your exposure level and risk increase.

The prevalence of skin cancer and sun exposure are closely linked. The incidence of melanoma skin cancers in Caucasian populations generally increases with decreasing latitude, with the highest recorded incidence occurring in Australia⁸. Their annual rates are ten and over 20 times the rates in Europe for women and men, respectively.

The American Institute for Cancer Research investigated the melanoma rates⁹ for both sexes in 2018. In both males and females, Australia had the highest incidence rate, followed by New Zealand. The U.S. ranked 17th.


Moles are benign and non-cancerous pigmented tumors. Babies are not usually born with moles, and they will often begin to appear in children and over the course of one’s life. While most moles will never cause any problems, an individual who has many moles is more likely to develop melanoma.

Atypical moles¹⁰, also known as dysplastic nevi, are moles that look similar to normal moles but have additional features of melanoma. Atypical moles are often larger than other skin moles and usually have an abnormal shape or color. They can also appear on skin exposed to the sun and skin that is usually covered, such as on the buttocks or scalp.

While researchers and scientists are still investigating what exactly causes atypical moles, many believe the reason they develop is due to a combination of genetic and environmental factors.

People with atypical mole syndrome¹¹ are at a high risk of developing melanoma. Atypical mole syndrome is characterized by the following:

  • 50 (or more) moles

  • One or more atypical moles

Atypical moles often run in families, and only a small percentage of dysplastic nevi may develop into melanomas. However, most atypical moles never become cancer, and many melanomas seem to arise without a pre-existing mole.

While the chance of any single mole turning into cancer is not high, anyone with lots of irregular or large moles has an increased risk for melanoma and should get checked out by a health professional.


You might be wondering if skin cancer is genetic. If you have a high prevalence of atypical moles with a family history¹² of melanoma, you have an increased risk of developing melanoma.

Also, if you have any of the following common melanoma risk factors¹³ plus atypical moles, it’s recommended to get checked out.

  • Fair skin, with light eyes or hair

  • Freckles

  • Multiple moles over your body

  • A family or personal history of melanoma or non-melanoma skin cancer

  • Photosensitivity

  • Inability to tan

  • Repeated sunburns

While you may not have a family history of skin cancer, if you have atypical moles, you will have an elevated risk of developing melanoma.

The lowdown

Various external and genetic factors can cause skin cancer. All these factors increase the risk of developing moles and skin mutations, which can result in melanoma.

If you want to reduce your risk of developing skin cancer during your lifetime, protect yourself from these risk factors and get checked out by a health professional regularly.

Have you considered clinical trials for Skin cancer?

We make it easy for you to participate in a clinical trial for Skin cancer, and get access to the latest treatments not yet widely available - and be a part of finding a cure.

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