You may have seen the theory that the increase in microcephaly in South America is caused not by the Zika virus, but by a pesticide called pyriproxyfen that officials have been putting into water to kill mosquitoes.

This theory has been circulating in a number of conspiracy-happy publications — often along with the claim that the pesticide is made by Monsanto — and getting lots of play on social media (also conspiracy-happy). But now the theory has a more significant backer: The Brazilian state of Rio Grande do Sul has suspended use of the pesticide in drinking water. “Although we have no indication that the larvicide has a link with microcephaly cases, it is also true that we do not have any strong evidence that it has no links,” the state’s health secretary,  João Gabbardo Dos Reis, told the Wall Street Journal.

This is just nuts.

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A reasonable person might ask, why? Intuitively, from afar, it makes a lot of sense to stop using this pesticide until we figure out what’s going on. After all, we’re not totally sure that Zika is causing the microcephaly yet. So why not just err on the side of caution?

Because “caution” — in this case, not using the pesticide — is more likely to cause more harm than the alternative. Less pesticide means more mosquitoes and more mosquito-born diseases. It’s equivalent to Donald Trump suggesting that we block Muslims from entering the U.S. “until we are able to determine and understand this problem,” without any apparent awareness that this caution will hurt any number of blameless people. Communicating about risk is difficult because the human brain is good at assessing one risk at a time, but not so good at weighing every possible risk at once. We focus on one threat and ask:

“Is there some risk there, brain?”

“Hmm, I suppose there’s possibly a little risk,” the brain will reply.

“Well, best avoid it then!”

This process depends on the fiction that risk is avoidable. But it’s not. There are risks everywhere you look. Look to your left and, let’s imagine, there’s a barbed wire fence — better not go that way. But look to your right, and there’s a field that looks like prime rattlesnake habitat — could be risky! Oh, and now you can see that something fast and loud is approaching: Did I mention that you are standing on train tracks?

When I’m looking at risk assessments, I pay the most attention to the people who are doing a holistic accounting of the situation — whose primary interest is in making sure you get off those tracks safely. I’m much less interested in the assessments of people trying to raise awareness of any one particular threat — the anti-barbed wire activists. It’s not that those people are necessarily wrong (barbed wire really can cause some nasty injuries); but they are just less likely to weigh all possible risks.

The origin of the pesticide theory was, surprise surprise, a small physicians’ group that campaigns against pesticides. The group hasn’t done any epidemiology to demonstrate that people exposed to the pesticide are more likely to have babies with microcephaly; it has simply laid out an argument. The mainstream groups, looking at this problem holistically, have said there’s much better evidence that mosquitoes are hurting people than the evidence (and there’s no evidence, really) that the stuff killing mosquitoes is hurting people. Here’s the Wall Street Journal:

Brazil’s Health Ministry issued a statement that there is no evidence linking larvicide to microcephaly. “Unlike the relationship between the Zika virus and microcephaly, which has had its confirmation attested in tests that indicated the presence of the virus in samples of blood, tissue and amniotic fluid, the association between the use of pyriproxyfen and microcephaly has no scientific basis,” the ministry said …

Another group, the Brazilian Association of Collective Health, which advocates against the widespread use of pesticides, and is cited in the Argentine physicians group’s report, also denounced the assertion of any link between microcephaly and pesticide use. It cautioned against “spreading untruths and content without any (or enough) scientific basis.”

Perhaps the biggest problem with the theory that this pesticide is causing microcephaly is that it’s used in lots of places where there has been no increase in microcephaly. Farmers use it in the U.S. Pyriproxyfen is one of the safer pesticides out there. It breaks down in sunlight. Its toxicity is low enough that the EPA allows farmers to spray it on crops just seven days before harvest. In South America, officials started using the pesticide more than a decade before the microcephaly surge.

One other thing: Pyriproxyfen isn’t actually manufactured by Monsanto, or even a subsidiary of Monsanto, as journalist Mark Lynas found:

In its Zika press release, the group claimed that the larvicide “pyroproxyfen” (spelt wrong, incidentally) “is manufactured by Sumimoto Chemical, a Japanese subsidiary of Monsanto”.

Scary! Everyone knows Monsanto is evil — so blaming them and some Japanese ‘chemical’ company is a great way to confirm biases for anti-GMO types and chemophobes in general. Except that it’s completely wrong. For a start the company is called Sumitomo, not Sumimoto. More importantly, as a Monsanto spokesperson told me: “Sumitomo is not owned by Monsanto. However, we do have a long-standing business relationship — they supply us with a couple of herbicides.” Guilty! Hang them!

So in reality Monsanto has nothing to do with any of this, but the antis get their headline: “Argentine physicians claim Monsanto larvicide is true cause of microcephaly.” And Facebook does the rest.

There’s a reason purveyors of this theory have stretched to connect Monsanto to the theory. As the New York Times points out:

Though Brazil is at the center of an epidemic now affecting more than two dozen countries, many of the dubious claims about Zika are born abroad, their purveyors a well-known coterie of critics of genetically modified crops and creatures.

With reputable-sounding names like The Ecologist and Global Research, they produce slick websites that weave facts, half-truths and pseudoscientific analysis into sinister assertions. They trace the hidden hand of “Big Pharma” spreading disease for profit and claim that billionaires like Bill Gates are closeted eugenicists seeking to address overpopulation by promoting poisoned childhood vaccines.

Environmentalists called out The Ecologist for trumpeting another flimflam theory — that the microcephaly was caused by GMO mosquitoes — and the magazine backtracked a bit. But the publication jumped on this new theory just as quickly.

As Grist’s Aura Bogado observed, there’s an undercurrent of racism in the Zika scare. From our comfortable seats we superimpose the threats most present in our own minds onto the crisis. If we were instead focused on the needs of the people in danger, we might see that Zika itself is a relatively minor risk — even if you consider only mosquito-born diseases, there are other disease risks that kill many more people every year. Abandoning mosquito-control efforts would be a public health disaster.

From a relatively safe position in the U.S., it’s all too easy to see pesticides purely as a risk. And there is, indeed, always risk associated with using pesticides. But it’s imperative that we weigh that risk against the risks of not using them.

Using pesticides can injure farmworkers and damage the environment. Failure to use pesticides can make nutritious food unaffordable to low-income families, hurt the environment by expanding the amount of land needed for agriculture, and facilitate the spread of disease. There’s no black and white, no good and evil, here. We can’t simply wait until we figure everything out. Instead, we must proceed, with great care and deep empathy, using the best evidence we have.