Researches were able to identify a number of risk factors which can cause melanoma. There are four categories like environmental, genetic, immunosuppressive, and previous melanoma.

The people who are at most risk for melanoma are those:
1. People who had frequent or long-term exposure to sunlight due to working or leisure activities.

2. People who have family history of melanoma. Genetic risk factors are said to strongly correlate to a person's risk of developing melanoma. These factors are family history of melanoma, moles, color of the skin, hair and eyes.

*Family History: there are 5% to 10% of people who developed melanoma have a blood relative like parent, brother, sister, child, grandparent, aunt or uncle how have melanoma.Research is being conducted to be able to determine how melanoma is inherited.

3. Those with fair complexion and exposed to intense solar radiation can developed a number of acquired pigmented moles and can induce atypical moles to develop melanoma.

4. People who have atypical moles. There are many studies that showed the risk of melanoma when a person has 50 or more moles, atypical moles, large moles at birth. People who have many as 50 or more moles are at greater risk for developing melanoma. Researchers also found out that 1/3 of non-familial melanomas develop in atypical moles which is typically called by dermatologists as dysplastic nevi.

Another group of people who are at risk are people with psoriasis. For some people with mild psoriasis light therapy is prescribed which involves being exposed to ultraviolet light. The key to success with light therapy is consistency so you are constantly being exposed to ultraviolet light. I have to go to my dermatologist every six months to be checked over for skin cancers.

From what I have learned, people that have had more than 1 severe sunburn have the risk of having skin cancer. This is why sun screen is so important. Each time there is sun damage the risk increases for skin cancer to appear.

Other people answering this question have gone over other possible causes like family history, but skin damage really is an especially major factor. While many people love the look you get from being tanned, skin damage really is skin damage. Some people even burn on purpose so that the burn will turn into a tan and they'll get darker, faster. It doesn't take much to start raising your risk of developing skin cancer, and the more you tan the higher the chances are.

I'm not saying there aren't other factors at play, but those who tan heavily have a much higher risk. While I'm sure there are some people who tan frequently and will never develop melanoma, you can't always beat the odds.