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 many 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.
Several risk factors can 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 beds and sun lamps are also sources of UV rays.
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.
The nature of the UV exposure may play a role in melanoma development. For example, the development of melanoma on the trunk (chest and back) and legs has been linked to frequent sunburns (especially in childhood). This might also have something to do with the fact that these areas are not constantly exposed to UV light. Some experts think that melanomas that start in these areas are different from those on the face, neck, and arms, 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.
To learn more about the effects of UV rays on the skin and what you can do to protect yourself and your loved ones, see Skin Cancer Prevention and Early Detection.
Moles
A mole (also known as a nevus) is a benign (non-cancerous) pigmented tumor. Babies are not usually born with moles; they often 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.
Atypical moles (dysplastic nevi): These moles 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.
Dysplastic nevi often run in families. 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.
Dysplastic nevus syndrome (also known as familial atypical multiple mole melanoma syndrome, or FAMMM): People with this inherited condition have many dysplastic nevi and at least one close relative who has had melanoma.
People with this condition have a very high lifetime risk of developing melanoma, so they need to have very thorough, regular skin exams by a dermatologist (a doctor who
specializes in skin problems). In some cases, full body photos 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 is 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 don’t have a chance to become cancer. 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 much 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 one 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, certain gene changes (mutations) that run in a family, or a combination of factors.
Most experts do not recommend that people with a family history of melanoma have genetic testing to look for mutations, as it’s 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 avoiding 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 or other skin cancers
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 had basal or squamous cell skin cancers are also at increased risk of getting melanoma.
Weakened immune system
A person’s immune system helps fight cancers of the skin and other organs. People with weakened immune systems (from certain diseases or medical treatments) are more likely to develop many types of skin cancer, including melanoma.
For example, people who get organ transplants are usually given medicines that weaken their immune system to help prevent them from rejecting the new organ. This increases their risk of developing melanoma.
People infected with HIV, the virus that causes AIDS, often have weakened immune systems and are also at increased risk for melanoma.
Older age
Melanoma is more likely to occur in older people, but 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.
Male gender
In the United States, men have a higher rate of melanoma than women, although this varies by age. Before age 45, the risk is higher for women; after age 45 the risk is higher in men.
Xeroderma pigmentosum
Xeroderma pigmentosum (XP) is a rare, inherited condition that affects skin cells’ ability to repair damage to their DNA. People with XP have a high risk of developing melanoma and other skin cancers when they are young, especially on sun-exposed areas of their skin.
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