These pesticides are called pyrethrins. They're based on a natural nerve agent from the chrysanthemum plant. In the last two decades they've largely replaced an earlier class of household pesticides, organophosphates,like DDT, which were developed from World War II nerve gas.
The pyrethrins are considered safer because they're not readily absorbed through the skin, they're eliminated quickly from the body, and they break down quickly in the environment.
But the Center for Public Integrity documented a three-hundred-percent jump in reported human health problems from this group of pesticides over the last decade. And some scientists are concerned there might be long-term issues that haven't showed up yet.
It's likely that exposure incidents are under-reported, according to Minnesota Department of Health, environmental research scientist Chuck Stroebel.
"People may not recognize the symptoms, or associate them with a pesticide exposure, because sometimes the symptoms are more subtle in nature. If it's an acute exposure, the symptoms become more obvious, and are more likely to be recognized."
The most likely source of exposure for most people is from household products like ant and roach killer, flea collars and shampoos for pets, and shampoo for killing lice.
People usually run into problems when they don't follow the directions. Symptoms show up on the skin or in the respiratory system, Stroebel says.
“Who's playing in the carpet where the pet tracks in residues from the yard and they lodge in carpet fibers? It's kids.”David Wallinga
"There are some reports of contact dermatitis, skin-type reactions, but we do know that the pyrethrins are not readily absorbed across the skin; it's more of a localized effect. And also respiratory or eye irritation if there was any direct contact with the product. And potentially, people with asthma could be more susceptible to any kind of irritant."
The Hennepin Regional Poison Control Center collects data from all over Minnesota. Two hundred sixty three people called to report a reaction to a pyrethrin-type pesticide in 2006, according to the center. That compares to 62 reports for the older organophosphates.
The Minnesota Department of Agriculture also takes calls -- usually from people exposed to pesticides in farm fields. The Ag Department took only one call on pyrethrin pesticides in each of the last two years.
Some people may call the 800-number listed on the can of roach spray or other product. With all these uncoordinated reporting centers, no one really knows how many episodes there are.
The report from the Center for Public Integrity calls for a uniform reporting system for pesticide exposure, with guidelines provided by the federal government.
It may be years before we know how safe -- or dangerous -- these pesticides are. The Environmental Protection Agency continued to allow the older organophosphates for home use after problems were well-documented, critics say.
Although pyrethrins are known to interfere with the nervous system, the EPA doesn't require any tests to see how it might affect young, developing brains, according to David Wallinga, a physician and director of the Food and Health program at the Institute for Agriculture and Trade Policy, a Minneapolis-based non-profit. Children are inherently more vulnerable to such chemicals, he says, and they also tend to be exposed to more of them.
"Who hugs their pet, and plays with their pet more? Kids. Who's playing in the carpet where the pet tracks in residues from the yard and they lodge in carpet fibers? It's kids."
Young children can also be poisoned directly by sprays that aren't properly stored.
The EPA says it will review its data on human health effects of pyrethrin pesticides sooner than it had planned to, as a result of the report from the Center for Public Integrity.
Some states, such as California and Texas, require doctors to report pesticide exposure to a state clearinghouse. That helps raise awareness and accuracy of reporting. So far, Minnesota does not have such a requirement.