They added that tests they performed revealed that much of the DHA applied to skin actually ended up in the living layers of skin.
They concluded: "This leaves about 11 percent of the applied DHA dose absorbed remaining in the [living] epidermis and dermis."
Four years after the report was issued, the FDA wrote a follow-up paper based on the same data, concluding that "probably" only 0.5 percent of each application of DHA becomes "systemically available," meaning distributed throughout the body after reaching the bloodstream.
The agency concluded that 0.5 percent of an applied dose of DHA was poor absorption, and no further testing was done to check for actual toxicological impacts on the human body. The thinking was that because only a little bit of DHA entered the bloodstream, the health risk would be very low.
However, any absorption into the living areas of the skin could be pose a potential risk, even if none of it made it into the bloodstream, said Dr. Darrell Rigel, an NYU professor of dermatology. The fact that some does potentially get into the bloodstream raised additional red flags for him that he said needed to be further explored.
Rigel was especially concerned for repeated users of the product and those in higher-risk groups such as pregnant women or young children.
Girls as young as 4 years old who compete in beauty pageants are known to be spray tanned by their moms, who believe the tan to be a completely safe way to give their children a darker glow.
Rigel believes the FDA paper, combined with other literature he reviewed, would surprise many of his colleagues in the medical field. He said the papers were enough to make him change what he will tell his patients about spray tanning.
"What you showed me certainly leads me to say I have to rethink what I'm doing and what I'm saying because there's ... a real potential problem there," he said. "I feel that I must give my patients the information that you've given to me, because I think it is valid."
Following receipt of the 1999 FDA report, ABC News located nine other studies performed mostly by non-government university researchers on DHA. ABC News asked Rigel and five other medical experts to review the papers and anything else they could find on their own, and to offer their analysis about potential health risks.
Before he read all of the papers, Rigel said, he would "tell my patients what every other dermatologist tells them: 'If you want to be tanned, [tanning with DHA] is effective, it's not being absorbed and there's no long-term problems.' After reading these papers, I'm not sure that's true anymore."
"A potential problem has been identified and for public safety, more studies should be done," added Rigel, a former president of the three largest dermatological groups in the nation: the American Academy of Dermatology, the American Dermatological Association, and the American Society for Dermatologic Surgery.
"The concern here is we never thought this was getting absorbed," he said. "We thought it's binding to the surface of the skin and that's where the stain is. So this is ... news that, in fact, it is penetrating beyond that."
ABC News also presented the panel of experts with information about some studies that found no carcinogenic or potential cancer-causing impacts of DHA, such as when it was tested on mice.
However, that same FDA report from the 1990s raised questions about whether some of those tests came up negative simply because the DHA never absorbed into the skin of the particular type of mice tested.
Dr. Lynn Goldman, the dean of the School of Public Health and Health Services at George Washington University, reviewed the same group of papers and said that DHA tested positive for mutating genes in far too many different types of studies to reject concerns about its health implications.
"The substance seems to have a potential for what they call creating mutations or changing DNA in living cells, which is a serious problem and needs to be further investigated, yet hasn't been," she said.
"What we're concerned about is not so much that reaction that creates the tanning, but reactions that may occur deeper down with living cells that might then change DNA, causing a mutation and what the possible impacts of that might be," she said. "I'd be very concerned for the potential of lung cancer."
Researchers should, however, not just be concerned about cancer, but other health effects such as birth defects, especially if a woman who was pregnant was spray tanning and allowing the mist to get inside her body, Goldman said.