Howie Diamond, 22, left, Luke Dash, 21, center, and Ben Pollack, 23, right, soak up the sun at Will Rogers State Beach in Los Angeles. While they may be absorbing more vitamin D, they could be increasing their risk of developing skin cancer. (Krista Niles/Associated Press)

You probably know by now that making bad decisions when it comes to sun protection can be life threatening. While some people smartly skip the midday sun altogether, others work outdoors in tank tops every day or hit the beach with a bottle of baby oil, increasing their chances of developing skin cancer.

But it isn't all about daily habits — a portion of the risk has to do with culture and family history. Where we live (a result of latitude and long-term migration patterns), prevailing cultural beliefs (and the associated garb), and common vacationing habits all play a role in our chances of developing ailments related to sun-exposure.

Looking at data for regions around the globe, the countries with the greatest per-capita skin cancer burdens — attributable to solar ultraviolet (UV) radiation — include the United States, Canada and Cuba, as well as portions of the Pacific and, more surprisingly, Northern Europe.

The bottom of the list consists mainly of South Asian countries, including India, Maldives, Bhutan and Bangladesh.

Behind the numbers

To find out which countries had some of the biggest health problems due to the sun's UV radiation, we used a 2006 World Health Organization report that showed or estimated the extent of cutaneous malignant melanoma, squamous cell carcinoma and basal cell carcinoma (the three main types of skin cancer) in 14 different regions of the world, as defined by the WHO.

Rather than looking at mortality rates (since not all skin cancers are deadly), we ranked the regions' per-capita skin cancer burdens attributable to solar UV radiation using a metric known as disability-adjusted life years (DALYs). The term combines years of life lost and years lost to disability. We averaged the upper and lower estimates of the three cancers' burdens attributable to UV radiation in DALYs for each region and then corrected for its population.

Researchers relied on statistics and estimates of the disease burden from solar UV radiation for large regions because data for each country is not yet available. As a result, the region containing Australia, New Zealand and Japan did not rank quite as high as expected because of the inclusion of Japan, which has a low rate of disease attributable to UV radiation as well as a relatively large population, says Dr. Robyn Lucas, an epidemiologist at the National Centre for Epidemiology and Population Health at the Australian National University and one of four authors of the WHO report.

Australia and New Zealand have the highest incidence and mortality rates of melanoma in the world, according to Australia's Department of Health and Aging. In those two countries, the risk of developing melanoma before the age of 75 is one in 24 for males and one in 34 for females.

The blame game

Australians and Kiwis battling skin cancer today have their fair British and European ancestors to blame (in part), according to experts. Migration patterns over the past few hundred years have created a scenario in which most people's skin pigmentations are no longer suited to their environments — as is the case with Australians' and New Zealanders' ancestors coming, in large part, from the British Isles. Fair-skinned populations that migrated to areas with high ambient levels of solar ultraviolet radiation have experienced a jump in the incidence of both melanoma and non-melanoma skin cancers, Lucas says.

Likewise, even when the migration is short-lived it can have an impact. Countless fair-skinned residents of northern European countries regularly holiday in sunny locales, such as the south of France, and have a tendency to let their guard down, says Dr. Orit Markowitz, a clinical instructor at the Mount Sinai School of Medicine. In other words, they bask in the sun rather than take steps to protect themselves from it.

Studies have shown that while there is generally an increase in the incidence of melanoma as latitude decreases (closer to the equator), mortality from melanoma is four to six times higher in Nordic countries than in Mediterranean countries, according to the WHO. Given that melanoma is believed to be related to intermittent, intense sun exposure (especially for those who are fair), light-skinned northern Europeans who vacation in the sun are putting themselves at high risk.

It's a cultural thing

A region's cultural beliefs affect its burden of UV-related skin cancer too, says Dr. Henry W. Lim, chairman of the Department of Dermatology for the Henry Ford Health System and immediate past vice president of the American Academy of Dermatology. While many Americans still can't free themselves of the notion that a tan makes you look healthy (one reason why the country may have topped the list), in Asian countries, such as Japan and China, tanning is far less culturally acceptable. It's even believed to be associated with a lower socio-economic status, says Lim.

"The use of the parasol for photo-aging protection is very common among women there," Lim says, "while it's rare in the U.S."

Along those lines, many countries with large Muslim populations, such as Maldives, Bangladesh, Indonesia and Somalia, fell toward the bottom of the list, likely because of their skin pigmentation, a traditional style of dress that's protective against high ambient UV radiation and an adaptation in behavior over the years. In other words, you probably won't find many natives of these areas lying out on the beach.

Latitude and altitude also play roles, since the sun is more direct and UV radiation levels higher in latitudes close to the equator; a thin atmosphere absorbs less UV radiation at high altitudes.

Of course, many countries with high rates of skin cancer, such as Australia, have been working hard in recent years to raise awareness, particularly among young people, about the risks associated with sun exposure. The country's National Skin Cancer Awareness Campaign, for instance, aims to make it socially acceptable for people to adopt multiple sun protection behaviours, rather than just relying on sunscreen.

But, experts say, there's still plenty of room for improvement.

"People have got the message," Lucas says, "but I don't think it always translates into behaviour."