What are the risk factors for melanoma skin cancer?
A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, like smoking and excess sun exposure, can be changed. Others, like a person’s age or family history, can’t be changed.
But having a risk factor, or even several risk factors, does not mean that you will get the disease. And some people who get the disease may have few or no known risk factors. Even if a person with melanoma has a risk factor, it’s often very hard to know how much that risk factor might have contributed to the cancer.
Scientists have found several risk factors that could make a person more likely to develop melanoma.
Ultraviolet (UV) light exposure
Exposure to ultraviolet (UV) rays is a major risk factor for most melanomas. Sunlight is the main source of UV rays. Tanning lamps and beds are also sources of UV rays. People who get a lot of UV exposure from these sources are at greater risk for skin cancer, including melanoma.
While UV rays make up only a very small portion of the sun’s rays, they are the main cause of the damaging effects of the sun on the skin. UV rays damage the DNA of skin cells. Skin cancers begin when this damage affects the DNA of genes that control skin cell growth.
There are 3 main types of UV rays:
- UVA rays cause skin cells to age and can cause some damage to the cells’ DNA. They are linked to long-term skin damage such as wrinkles, but are also thought to play a role in some skin cancers.
- UVB rays can cause direct damage to skin cells’ DNA, and are the main rays that cause sunburns. They are also thought to cause most skin cancers.
- UVC rays don’t get through our atmosphere and therefore are not present in sunlight. They do not normally cause skin cancer.
Both UVA and UVB rays damage skin and cause skin cancer. UVB rays are a more potent cause of at least some skin cancers, but based on what is known today, there are no safe UV rays.
The amount of UV exposure a person gets depends on the strength of the rays, the length of time the skin is exposed, and whether the skin is protected with clothing or sunscreen.
The nature of the UV exposure may play a role in melanoma development. Many studies have linked the development of melanoma on the trunk (chest and back) and legs to frequent sunburns (especially in childhood). The fact that these areas are not constantly exposed to UV light may also be important. Some experts think that melanomas in these areas are different from those that start on the face and neck, where the sun exposure is more constant. And different from either of these are melanomas that develop on the palms of the hands, soles of the feet, under the nails, or on internal surfaces such as the mouth and vagina, where there has been little or no sun exposure.
For information on how to protect yourself and your family from UV exposure, see the section “Can melanoma skin cancer be prevented?”
A nevus (mole) is a benign (non-cancerous) pigmented tumor. Moles are not usually present at birth but begin to appear in children and young adults. Most moles will never cause any problems, but a person who has many moles is more likely to develop melanoma.
Dysplastic nevi: Dysplastic nevi (nevi is the plural of nevus), also called atypical nevi, often look a little like normal moles but also have some features of melanoma. They are often larger than other moles and have an abnormal shape or color. (See the section “Signs and symptoms of melanoma skin cancer” for descriptions of how moles and melanomas look.) They can appear on skin that is exposed to the sun as well as skin that is usually covered, such as on the buttocks or scalp.
A small number of dysplastic nevi may develop into melanomas. But most dysplastic nevi never become cancer, and many melanomas seem to arise without a pre-existing dysplastic nevus.
In people who have dysplastic nevus syndrome, a condition that causes them to have many dysplastic nevi, the lifetime risk of melanoma may be higher than 10%. Dysplastic nevi often run in families. Someone with many dysplastic nevi and with several close relatives who have had melanoma has a very high lifetime risk of developing melanoma.
People with dysplastic nevus syndrome need to have very thorough, regular skin exams by a dermatologist (a doctor who specializes in skin problems). In some cases, full body photographs are taken to help the doctor recognize if moles are changing and growing. Many doctors recommend that these patients be taught to do monthly skin self-exams as well.
Congenital melanocytic nevi: Moles present at birth are called congenital melanocytic nevi. The lifetime risk of melanoma developing in congenital melanocytic nevi has been estimated to be between 0 and 10%, depending on the size of the nevus. People with very large congenital nevi have a greater risk, while the risk is less for those with small nevi. For example, the risk for melanoma in congenital nevi smaller than the palm of your hand is very low, while those that cover large portions of back and buttocks (“bathing trunk nevi”) have significantly higher risks.
Congenital nevi are sometimes removed by surgery so that they do not have a chance to become cancerous. Whether doctors advise removing a congenital nevus depends on several factors including its size, location, and color. Many doctors recommend that congenital nevi that are not removed should be examined regularly by a dermatologist and that the patient should be taught how to do monthly skin self-exams.
Again, the chance of any single mole turning into cancer is very low. However, anyone with lots of irregular or large moles has an increased risk for melanoma.
Fair skin, freckling, and light hair
The risk of melanoma is more than 10 times higher for whites than for African Americans. Whites with red or blond hair, blue or green eyes, or fair skin that freckles or burns easily are at increased risk.
Family history of melanoma
Your risk of melanoma is greater if 1 or more first-degree relatives (parent, brother, sister, or child) has had melanoma. Around 10% of all people with melanoma have a family history of the disease.
The increased risk might be because of a shared family lifestyle of frequent sun exposure, a family tendency to have fair skin, or a combination of factors. It may also be due to gene changes (mutations) that run in a family. Gene mutations have been found in anywhere from about 10% to 40% of families with a high rate of melanoma.
Most experts do not recommend that people with a family history of melanoma have genetic testing to look for mutations, as it is not yet clear how helpful this is. Rather, experts advise that they do the following:
- Have regular skin exams by a dermatologist
- Thoroughly examine their own skin once a month
- Be particularly careful about sun protection and avoid artificial UV rays (such as those from tanning booths)
(For more information on genetic testing, see “Can melanoma skin cancer be prevented?”)
Personal history of melanoma
A person who has already had melanoma has a higher risk of getting melanoma again. About 5% of people with melanoma will develop a second one at some point.
People who have weakened immune systems or who are being treated with medicines that severely suppress the immune system, such as organ transplant patients, have an increased risk of melanoma.
Although melanoma is more likely to occur in older people, it is also found in younger people. In fact, melanoma is one of the most common cancers in people younger than 30 (especially younger women). Melanoma that runs in families may occur at a younger age.
In the United States, men have a higher rate of melanoma than women overall, although this varies by age. Before age 40, the risk is higher for women; after age 40 the risk is higher in men.
Xeroderma pigmentosum (XP) is a rare, inherited condition resulting from a defect in an enzyme that normally repairs damage to DNA. People with XP have a high risk for developing melanoma and other skin cancers at a young age. Because people with XP are less able to repair DNA damage caused by sunlight, they can develop many cancers on sun-exposed areas of their skin.
Last Medical Review: 10/29/2013
Last Revised: 10/29/2013