You might expect a sunny sojourn to leave you with sand in your shoes or a lingering margarita headache, but 23-year-old Lisa Knightly* returned from the Caribbean with a life-threatening souvenir: melanoma.

In November 2011, prior to the holiday, "I noticed a new mole on my lower shin," says the Hamilton-based student. "My family doctor measured it and said not to worry."

But after a week of intense sun, Lisa's mole started to swell. "I noticed it had changed, but since my doctor wasn't originally alarmed, I put off going back to get it checked – something I deeply regret now," she admits. "When I finally made a followup appointment in early March 2012, I was referred to a dermatologist, who performed a precautionary biopsy."

A few days later, Lisa received a call with the troubling news. "When I heard the word 'melanoma,' I was so shocked." Melanoma is the deadliest of skin cancers. It moves fast, spreading to other vital organs. "I was really scared. I truly thought I was going to die." Lisa bounced between family doctors, dermatologists, oncologists and plastic surgeons until her mother advocated on her behalf to secure an accelerated surgery date. Lisa has been cancer-free since April 2012.

Danger rays
According to the Canadian Dermatology Association (CDA), more than 80,000 cases of skin cancer were diagnosed in Canada in 2011 – more than breast, lung and prostate cancers combined. Melanoma makes up about 5,500 of those cases and causes nearly 1,000 deaths per year. It's the eighth most deadly cancer in Canada, and sunshine is a key factor. "Over years, exposure to UV rays – high intensity or not, periodic exposure or not – damages our DNA, causing cells to mutate so they don't know when to stop dividing," explains Dr. Jaggi Rao, a professor of dermatology at the University of Alberta. The uncontrolled growth displaces normal cells, creating tumours. UVB rays, which are shorter in wavelength than UVA, are largely responsible for sunburns on the surface of the skin; UVA rays penetrate deeper, triggering much of the DNA damage.

Indoor tanning is no better. According to CDA research, using tanning beds before age 35 significantly increases the risk of developing skin cancer. Health Canada now requires salons and bed manufacturers to warn customers of the risks. Nova Scotia, Newfoundland, British Columbia and Quebec ban people under 18 from using tanning salons. And the World Health Organization actually classifies tanning beds as "carcinogenic to humans," a designation that also applies to arsenic, asbestos, tobacco and plutonium.

Who's at risk?
UV rays are colour-blind: Any skin tone can be damaged. "The effects are microscopic and invisible – no matter if you're very fair or very dark – and are often delayed by months or years," says Rao. "Like heart disease, these slowly accumulating biological events are difficult to appreciate until it's too late." The standard theory says everyone faces two risk factors.

"Hit one is genetic: You must have the genes that allow this to occur. Hit two is environmental: Exposure to a trigger such as a sunburn or carcinogen. Cancer will only occur if both hits are accomplished, not just one."

Protecting yourself and your family
But there is some good news. Dermatologists agree that, when detected early, 90 percent of skin cancers can be cured. That's why self-monitoring is so important. "Probably more than 95 percent of skin cancers are brought to the attention of doctors by the patients themselves," says Rao.

Beyond vigilance, sunscreen is your most valuable shield. "The best sunscreen? One that you'll actually use," says Dr. Nowell Solish, a dermatologist in Toronto. "It should say broad-spectrum on the label to protect against both UVA and UVB, and it should have a minimum of SPF 30. It also helps to stay covered up with a hat and sunglasses, and avoid the sun's strongest hours, between 10 a.m. and 2 p.m."

Generously slather on sunscreen  – think of it like icing a cake – in a thick layer, then work it into the skin. Reapply every two hours, especially if you're perspiring or swimming. For kids, Solish recommends using spray sunscreens, because they don't feel as heavy on the skin.

The scar on Lisa's leg is a daily reminder of her skin scare. "I had gone virtually my entire life unprotected," she says. "Now, the first thing I do when I wake up is apply sunscreen over my entire body." Lisa tracks her moles, covers up when outdoors and sees her doctors regularly. "Many of my friends still go to tanning beds," she says. "They think it will never happen to them...but it can happen to anyone."

* Name was changed.

If you still want to learn more, here's what you need to know about skin cancer. Check out these cancer tests you need to know about to keep your body healthy. 

This story was originally titled "Overexposed: Are you safe?" in the July 2013 issue. Subscribe to Canadian Living today and never miss an issue!