Skin cancers can be divided into two main groups: melanoma and non-melanoma. In 2018, melanoma accounted for about 22 per cent of skin cancer diagnoses, and non-melanoma tumours accounted for about 78 per cent of skin cancer diagnoses. The most common non-melanoma tumours are basal cell carcinoma and squamous cell carcinoma.
Incidence
Melanoma is the 19th most common cancer in men and women, with nearly 300,000 new cases worldwide in 2018.
Non-melanoma skin cancer is the 5th most commonly occuring cancer in men and women, with over 1 million diagnoses worldwide in 2018. However, it is not usually included in estimates for global and national cancer rates. The data on non-melanoma skin cancer is usually less accurate and less complete than for other cancers.
Lifestyle factors and skin cancer risk
In the Continuous Update Project (CUP) – the world’s largest source of scientific research on cancer prevention and survivorship through diet, nutrition and physical activity – we analyse global research on how certain lifestyle factors affect the risk of developing skin cancer. This webpage forms part of the World Cancer Research Fund/American Institute for Cancer Research Third Expert Report Diet, Nutrition, Physical Activity and Cancer: a Global Perspective.
Findings on skin cancer
There is strong evidence that:
- drinking water contaminated with arsenic INCREASES the risk of skin cancer
- being tall INCREASES the risk of malignant melanoma
- beta carotene (as high-dose supplements) has no substantial effect on the risk of non-melanoma skin cancer
There is some evidence that:
- drinking coffee might decrease the risk of malignant melanoma in women and might decrease the risk of basal cell carcinoma in men and women
- consuming alcoholic drinks might increase the risk of malignant melanoma and basal cell carcinoma
- being tall might increase the risk of basal cell carcinoma
- greater birthweight might increase the risk of malignant melanoma
The panel judged the evidence and drew conclusions in March 2017. The conclusions drawn form part of the Third Expert Report.
Other causes of skin cancer
In addition to the findings on diet, nutrition and physical activity outlined above, other established causes of skin cancer include:
- radiation
Over-exposure to certain types of light, such as ultra-violet rays from the sun or tanning devices, is the principal cause of melanoma and non-melanoma skin cancers.
- medication
Medicines used to suppress the immune system after organ transplantation are associated with increased risk of skin cancers, particularly squamous cell carcinoma.
- infection
Infection with human papilloma virus can cause squamous cell carcinomas of the skin, especially in people whose immune systems are compromised.
- occupational exposure
Exposure to specific chemicals used in the plastic and chemical industries – polychlorinated biphenyls – is strongly associated with an increased risk of skin cancer.
- genetics and family history
Some rare mutation in specific genes can lead to skin cancer. Having a family history of skin cancer also increases risk.
- skin pigmentation
Skin cancer is more common in lighter-skinned populations than in darker-skinned populations.
Pathogenesis
Exposure to UV radiation is the primary cause of skin cancer. The role of sun damage is supported by the association between measures of sun sensitivity and skin cancer incidence, which is higher in people who have pale skin that burns without tanning, blue eyes and red hair. Both the duration and severity of exposure is important: there is a dose–response relationship between the number of sunburn episodes during any life period (childhood, adolescence or adulthood) and the risk of melanoma.
UV radiation can induce cellular changes consistent with the hallmarks of cancer, including inducing genomic instability and mutation, resisting cell death, activating sustained proliferative signalling and cell growth, as well as initiating tumour-promoting inflammatory responses.
UV radiation can directly damage DNA and also create cellular environments which are damaging to DNA, for example through the generation of reactive oxygen species. The activation of chronic inflammatory pathways helps generate an environment conducive to cancer development and progression and is associated with progression from actinic keratosis to squamous cell carcinoma.
Overall, UV radiation has a range of effects on skin cells, affecting several metabolic pathways that together create a cellular microenvironment conducive to the development and progression of cancer. These effects may be modulated by genetic factors.
How the research was conducted
The global scientific research on diet, nutrition, physical activity and the risk of skin cancer was systematically gathered and analysed, and then independently assessed by a panel of leading international scientists in order to draw conclusions about which of these factors increase or decrease the risk of developing skin cancer.