After a winter that seemed to last forever, spring is finally here. Off come the fleeces, the sweatpants, the raincoats. On go the bikinis, the tank tops, the swim trunks and T-shirts. Every last inch of skin that can be decently exposed is put on display. And the feeling is glorious.

On a lazy Sunday afternoon, the grassy bank stretching along the length of the Avery Aquatic Center is thick with Stanford students enjoying the first few days of sun and hoping to catch the makings of a tan.

"There's this trend in America that the browner you are, the hotter you are," says Melissa Morales, a freshman relaxing by the pool with her girlfriends. She giggles. "I might as well capitalize on it."

A tan may bring on that summery glow, but invisible UVB rays are also at work, causing painful burns and peeling or blistering skin. This sun exposure is what puts the body at risk for skin cancer.

Susan Swetter, a dermatology professor and director of the Pigmented Lesion and Cutaneous Melanoma Center at the Stanford University Medical Clinic, says, "There's a clearly-established link between long-term sun exposure pre-cancers and skin cancer."

She explains that there are three main types of skin cancer: melanoma, basal cell carcinoma and squamous cell carcinoma.

Basal cell cancers are the most common type of skin cancer. These non-melanoma cancers arise from chronic sun exposure and are not uncommon in younger individuals.

They're "absolutely curable," says Swetter, "but they can cause local disfiguration, since they may bleed and ulcerate."

Other types of non-melanoma skin cancer include squamous skin cancer, which is also caused by chronic sun exposure but can spread throughout the body, increasing the patient's risk of serious illness.

Most risky are melanomas themselves, the result of "intermittent blistering sun burns." Melanoma is one of the most common types of cancer for both men and women and usually shows up on the back of both sexes or the legs of women. If caught early, however, melanomas have a good prognosis.

"The vast majority of melanomas are thin and curable," Swetter explains. But left alone, they can spread down into the skin, then to the body's lymph nodes and the lymphatic system, and thus become "potentially deadly."

The average age for skin cancer development is over 40, but younger individuals are susceptible to pre-cancers. And, Swetter notes, "Melanoma is certainly not unheard of in individuals in their late 20s and 30s. In fact, the rates appear to be on the rise in children."

Fair-skinned individuals with an abundance of moles and a family history of skin cancer are the most at risk, although fair skin in itself is a risk factor for non-melanoma skin cancer.

Of course, skin cancer of all types can be avoided by minimizing risky behavior. That means covering up with long sleeves, hats and pants, and slathering plenty of sunscreen on skin that remains exposed. Swetter recommends SPF 15 as a baseline, but advises SPF 30 since most individuals don't use nearly enough product.

"You need an entire palm-full for the body and about a teaspoonful for the face to provide adequate protection," she insists.

Meanwhile, over by the swimming pool, Stanford students are getting tanner by the minute. But not all of them are wearing sunscreen.

Kevin Iori is a senior who's bypassed the sunscreen. "I haven't gotten around to getting any," he says, "but I would wear it if I had it." Iori already knows a thing or two about pre-cancers. He had a "iffy" mole removed a few years ago.

Francois Conti, a doctoral student in computer science says that he's wearing SPF 8.

"My fiancee gave me SPF 30," he admits, "but I'm out of it."

As for sophomore Beth Thompson, she's wearing SPF 15.

"I'm concerned about burning," she says. "But I sit in the sun because it makes me happy."

While it may not be possible to resist the lure of the sun, individuals should be vigilant about watching for suspicious lesions. Swetter advises keeping an eye on unusual-looking moles that are asymmetrical in shape, dark in color (even red or blue) with irregular borders, a diameter larger than 6 millimeters or have changed shape over time.

For concerned individuals, the Stanford Comprehensive Cancer Center is hosting a morning of free skin cancer screenings. The event will take place this Saturday, May 13 from 9 a.m. to noon. Physicians will be on hand to take histories and examine patients for irregularities and skin blemishes. The entire exam takes less than five minutes and is entirely non-invasive.

"We like to host this event in May since it's the start of the sunny season," says Erika Smith, marketing manager for skin cancer screening.

"It's also an easy way to get checked out," Smith says. "Even if you have to wait in line for a few minutes, it's worth it to know that you're fine."

After all, she says, "Catching skin cancer in time can seriously save a life."