Risk factors are defined as any personal characteristics or habits, hereditary factors or environmental exposure that increase the likelihood of developing a disease.

The main risk factors for skin cancer are:

Three people with different skin colour

Skin type. People with light skin face a greater risk than individuals with darker skin tones. While the risk for those with light skin and blond or red hair is four times greater than for other white people with darker skin and dark hair. This is because dark-skinned people produce better quality melanin (eumelanin) which gives the skin and hair their darker tone. It also protects the skin from ultraviolet radiation. The white-skinned population is 20 more times likely to develop skin cancer than the population with black skin. Nevertheless, it is important to highlight that melanoma does in fact affect all races. 

Sun and risk or danger sign

Exposure to ultraviolet (UV) radiation. Regular, intense exposure to UV radiation, whether from the sun or an artificial source (UV lamps), is the main environmental risk factor for skin cancer. It has been shown that repeated, severe sunburns (ones that result in blistering), especially during childhood, increase the risk of developing skin cancer. Light-skinned people who burn easily or have a lot of freckles must be particularly careful when exposed to the sun. Intermittent exposure to intense sunlight, e.g., during summer months, is generally associated with the onset of skin cancer; however, some cases of melanoma are also related to continuous, year-round exposure to the sun, for example, in people who work outdoors. 

DNA molecule or helix

Personal/family history. The risk of developing a melanoma increases significantly for individuals who have one or more first-degree relatives (parent, sibling or child) with a history of the disease. Approximately 10% of all melanoma patients have a family history of skin cancer. 

Melanocyte or skin cell

Genetic mutations. Genetic mutations in skin cells can lead to a lack of control over growth mechanisms and result in skin cancer. Some of these mutated cells can remain dormant and do not grow for several years. That is why they say that the skin has a memory and sunburns can lead to skin cancer years after they occurred.

Immune system cell with antibodies

The immune system. The immune system plays a very important role in controlling and eliminating genetically altered cells. Therefore a decrease in the body’s immune function results in a greater risk of developing skin cancer, especially if the skin has already suffered an accumulation of alterations due to sun damage produced over the years.

Person with a mole on the neck

Moles. People with a lot of moles are 7–10 times more likely to develop a melanoma. Moles are coloured patches of skin. They may be pinkish, dark brown or the same colour as the rest of the skin. The medical term for a mole is melanocytic nevus (plural nevi).

The sun provides the energy needed for life to exist on Earth and is the principal factor in determining the planet’s climate and weather. The sun not only sends visible light to the Earth, but it also emits invisible radiation, which at high doses can have a negative impact on our health.

Solar radiation is comprised of a wide variety of rays; some are blocked by the ozone layer and others manage to reach the Earth’s surface. The radiation that reaches the Earth consists of visible, infrared (IR) and ultraviolet (UV) rays. UV radiation is further divided into UVA, UVB and UVC rays, according to their wavelength. UVC rays are absorbed by the ozone layer.

The intensity of solar radiation depends on diverse factors, such as the time of year, time of day, latitude, altitude, reflections from the Earth’s surface and meteorological conditions. 

Solar radiation perpendicular to the Earth

Height of the sun. The intensity of UV radiation increases as the sun’s altitude increases. Therefore, radiation intensity varies according to the time of day and year. With the exception of tropical regions, UV radiation is most intense when the sun is at its maximum altitude, at around solar noon during summer months. 


Latitude, solar radiation getting the ground in a perpendicular way

Latitude. The intensity of UV radiation is greater the closer you are to the equator. 

Sunbeams hitting different altitudes of the ground

Altitude. The atmosphere is thinner and absorbs less UV radiation at higher altitudes. UV radiation increases by 4% with every 300 metre increase in altitude.v

Cloudiness, rays of the sun refracted by a cloud

Cloud cover. Radiation is highest when there are no clouds, but levels can also be high under cloudy skies. Over 90% of radiation can pass through thin cloud coverage. 

Sunbeams bouncing off the ozone layer

Ozone. The ozone layer absorbs a portion of the UV radiation that would otherwise reach the Earth’s surface. The thickness of the ozone layer varies throughout the year and even over the course of a day.

Sun radiation reflected from the surface

Surface reflections. Different types of surface reflect or disperse UV radiation to different degrees. Fresh snow can reflect up to 80% of UV radiation, dry sand on the beach reflects approx. 15% and sea water foam around 25%.

UVA rays can produce damage such as ageing or skin cancer, while UVB rays are the main cause of sunburn. Approximately 10 times more UVA rays reach the Earth’s surface than UVB rays. UVC rays are absorbed by the Earth’s atmosphere and do not affect the skin.

What is Cancer?

General information about Cancer

Read more

Substantiated information by:

Eugenia Moliner Papell
Josep Malvehy Guilera

Published: 20 February 2018
Updated: 20 February 2018

The donations that can be done through this webpage are exclusively for the benefit of Hospital Clínic of Barcelona through Fundació Clínic per a la Recerca Biomèdica and not for BBVA Foundation, entity that collaborates with the project of PortalClínic.


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