DAYTONA BEACH, Fla. — Scientists in the safe confines of a hotel conference room issued a dire warning to thousands of sunbathers outside: The rays you soak in today will lead to the most vicious form of skin cancer 20 years from now.

The bad news came amid a flurry of new scientific papers discussed recently showing that incidences of skin cancers, especially malignant melanoma, the fastest spreading form, are rising with no change in sight.

New evidence also suggests that the depletion of the Earth’s ozone layer could be allowing increasing levels of ultraviolet rays to bombard the planet. Scientists believe the rays can damage DNA, overriding the body’s natural genetic abilities to repair damage to the skin.

Researchers, armed with evidence to illustrate the growing skin cancer rate, now say that excessive sun exposure during childhood and early adulthood may provide the strongest links to malignant melanoma later in life.

“The sun you get prior to the age of 20 is much more important in terms of getting skin cancer than the sun you get after that age,” said Dr. Darrell Rigel, a dermatology professor at New York University.

Malignant melanoma, Rigel said, is latent for about 20 to 30 years. People who sunbathed excessively in the 1960s and ’70s may soon begin to face the consequences, he warned.

An estimated 27,600 Americans will develop malignant melanoma this year and 6,300 will die of it, according to American Cancer Society projections.

Malignant melanoma, the worst form of skin cancer, is the type most likely to spread quickly, especially to lymph nodes and to the brain. For that reason, it is the deadliest.

The cancer tends to grow quickly, starting as a brown or black spot. It first grows horizontally on the skin’s surface and then expands vertically into the skin. But Rigel said it doesn’t have to be fatal.

“No one should die of melanoma. If you catch it early enough it can be treated,” he said.

Sunscreens, he said, help but they won’t protect against malignant melanoma completely. The only way to guard against that form of cancer is to avoid excessive exposure to “bursts” of sun such as those absorbed during sunbathing.

Speaking at the the 32nd annual Science Writers’ Seminar sponsored by the American Cancer Society, Rigel said that the chance of getting malignant melanoma is increasing.

In 1935, the average American had a 1 in 1,500 chance of getting the disease. This year, the chance is 1 in 120. And by the beginning of the next century, the odds will be 1 in 90, he said.

The malignant melanoma rate, he said, is increasing worldwide, even among black and other dark-skinned populations that were once thought to be immune to the cancer. The Japanese are the only population that has not shown an increase in that cancer, Rigel said.

New research also shows that young American women in their 20s and 30s are developing the cancer at an increasing rate, possibly because of excessive sunbathing during their childhood and teen years.

“When you’re a teen, you’re immortal,” Rigel said.