By age 20, the experts note, an American has typically received 80 percent of his or her lifetime exposure to skin-damaging ultraviolet rays from sunlight.

The high lifetime exposure in area A coincides with a clustering of observed lung cancer deaths.

At lifetime exposures increasingly greater than the reference exposure level, the potential for adverse health effects increases.

"The risk is from lifetime exposure," he said, "not one annual exposure."

The participants discussed their lifetime exposure to noise exceeding 80 decibels, about the noise level of city traffic.

Eighty percent of the typical American's lifetime exposure to cancer-causing ultraviolet radiation occurs before the age of 20.

While that was slightly higher than a state guideline for lifetime exposure, it was fully 3,000 times lower than the Federal occupational standard.

It could be that lifetime exposure to noise and other damaging factors slowly wear down the ears' delicate mechanics.

Similar estimates have not been calculated for melanoma, but it is estimated that people get about 80 percent of their lifetime exposure to sunlight during childhood.

The results of that example for a lifetime exposure (ages 0-70) are as follows: