Should a healthy-minded person drink? (Only in moderation.) Smoke? (Clearly not.) Eat oatmeal? (It can't hurt.) Stay out of the sun forever? (What?)
Yet another health debate has broken out, this time over whether sunblock really protects your skin.
Dermatologists are loathe to say any tan is safe. A tan is the body's response to the sun's injurious ultra-violet rays in which it releases a darkening pigment in the upper layer of skin to protect it.
But two epidemiologist brothers from the University of San Diego, Cedric and Frank Garland, have added more fuel to the fire by raising disturbing arguments that sunblock gives sun worshipers a false sense of security.
A Harvard University medical journal and various national magazines have publicized the Garlands' views, which argue that a surge in melanomas, the most dangerous form of skin cancer, has coincided with the advent of sunblock use.
Sunblocks prevent the body's natural defense, a tan, from forming, the Garlands say. They say the chemical creams screen out only part of the ultra-violet light spectrum that causes skin cells to mutate and become cancerous. And they say sunblocks may prevent the formation of Vitamin D needed for a healthy dermis.
Most dermatologists decry the Garlands' arguments as unscientific and irresponsible.
"They've been playing this game for four or five years. They've never done a study and the things that are printed are really editorials," said Darrell Rigel, a dermatologist and an expert on skin cancer at New York University Medical School.
The risk of melanoma correlates with the number of sunburns one has suffered over a lifetime, not those suffered in the last year or two, dermatologists say.
"Skin cancer is a serious thing: One American an hour dies," Rigel said in a telephone interview.
Questions over sunblock use are being raised just as summer arrives. And scientists warn that protection from the sun is needed more than ever because the Earth's protective ozone layer is thinning.
In the United States this year, there will be 700,000 new cases of the three types of skin cancers _ basal cell, squamous cell and melanoma. The last, melanoma, metastasizes in the body quicker and is expected to kill 6,800 Americans this year, mostly men over age 50. Skin cancer is also a very serious problem in Australia, and the number of cases is rising rapidly in New Zealand, Sweden and Israel.
Ruth Sykes of the American Academy of Dermatology says the group rejects the Garlands' views and urges sun lovers _ especially pale, sun-starved office workers _ to use sunblock and to wear hats when out in the sun. Dermatologists also wish people would not use artificial tanning beds.
"Skin cancers are caused by sudden bursts of sunlight that cause bad sunburns, especially in childhood and adolescence," Sykes said. "In fact, 25 percent of skin cancer victims are in their childbearing years."
The Garlands do not give interviews about the subject of skin cancer or the criticism they have received, an assistant said.
But medical ethicists, though unfamiliar with the Garlands' work, said contrary opinions are not unusual in the unscientific public arena where the truth of what is, or is not, healthy, can be a matter of conjecture.