I'm posting this because LessWrong was very influential on how I viewed parenting, particularly the emphasis on helping one's brain work better. In this context, creating and influencing another person's brain is an awesome responsibility.

It turned out to be a lot more anxiety-provoking than I expected. I don't think that's necessarily a bad thing, as the possibility of screwing up someone's brain should make a parent anxious, but it's something to be aware of. I've heard some blithe "Rational parenting could be a very high-impact activity!" statements from childless LWers who may be interested to hear some experiences in actually applying that.

One thing that really scared me about trying to raise a child with the healthiest-possible brain and body was the possibility that I might not love her if she turned out to not be smart. 15 months in, I'm no longer worried. Evolution has been very successful at producing parents and children that love each other despite their flaws, and our family is no exception. Our daughter Lily seems to be doing fine, but if she turns out to have disabilities or other problems, I'm confident that we'll roll with the punches.

Cross-posted from The Whole Sky.

Before I got pregnant, I read Scott Alexander’s excellent Biodeterminist’s Guide to Parenting and was so excited to have this knowledge. I thought how lucky my child would be to have parents who knew and cared about how to protect her from things that would damage her brain.

Real life, of course, got more complicated. It’s one thing to intend to avoid neurotoxins, but another to arrive at the grandparents’ house and find they’ve just had ant poison sprayed. What do you do then?

Here are some tradeoffs Jeff and I have made between things that are good for children in one way but bad in another, or things that are good for children but really difficult or expensive.

Germs and parasites

The hygiene hypothesis states that lack of exposure to germs and parasites increases risk of auto-immune disease. Our pediatrician recommended letting Lily playing in the dirt for this reason.

While exposure to animal dander and pollution increase asthma later in life, it seems that being exposed to these in the first year of life actually protects against asthma. Apparently if you’re going to live in a house with roaches, you should do it in the first year or not at all.

Except some stuff in dirt is actually bad for you.

Scott writes:

Parasite-infestedness of an area correlates with national IQ at about r = -0.82. The same is true of US states, with a slightly reduced correlation coefficient of -0.67 (p<0.0001). . . . When an area eliminates parasites (like the US did for malaria and hookworm in the early 1900s) the IQ for the area goes up at about the right time.

Living with cats as a child seems to increase risk of schizophrenia, apparently via toxoplasmosis. But in order to catch toxoplasmosis from a cat, you have to eat its feces during the two weeks after it first becomes infected (which it’s most likely to do by eating birds or rodents carrying the disease). This makes me guess that most kids get it through tasting a handful of cat litter, dirt from the yard, or sand from the sandbox rather than simply through cat ownership. We live with indoor cats who don’t seem to be mousers, so I’m not concerned about them giving anyone toxoplasmosis. If we build Lily a sandbox, we’ll keep it covered when not in use.

The evidence is mixed about whether infections like colds during the first year of life increase or decrease your risk of asthma later. After the newborn period, we defaulted to being pretty casual about germ exposure.

Toxins in buildings

Our experiences with lead (and lessons learned about how to reduce risk). Our experiences with mercury.

In some areas, it’s not that feasible to live in a house with zero lead. We live in Boston, where 87% of the housing was built before lead paint was banned. Even in a new building, we’d need to go far out of town before reaching soil that wasn’t near where a lead-painted building had been.

It is possible to do some renovations without exposing kids to lead. Jeff recently did some demolition of walls with lead paint, very carefully sealed off and cleaned up, while Lily and I spent the day elsewhere. Afterwards her lead level was no higher than it had been.

But Jeff got serious lead poisoning as a toddler while his parents did major renovations on their old house. If I didn’t think I could keep the child away from the dust, I wouldn’t renovate.

Recently a house across the street from us was gutted, with workers throwing debris out the windows and creating big plumes of dust (presumably lead-laden) that blew all down the street. Later I realized I should have called city building inspection services, which would have at least made them carry the debris into the dumpster instead of throwing it from the second story.

Floor varnish releases formaldehyde and other nasties as it cures. We kept Lily out of the house for a few weeks after Jeff redid the floors. We found it worthwhile to pay rent at our previous house in order to not have to live in the new house while this kind of work was happening.

Pressure-treated wood was treated with arsenic and chromium until around 2004 in the US. It often has a greenish tint, though it may not be obvious after fading or staining. Playing on playsets or decks made of such wood increases children’s cancer risk. It should not be used for furniture (I thought this would be obvious, but apparently it wasn’t to some of my handyman relatives).

I found it difficult to know how to deal with fresh paint and other fumes in my building at work while I was pregnant. Women of reproductive age have a heightened sense of smell, and many pregnant women have heightened aversion to smells, so you can literally smell things some of your coworkers can’t (or don’t mind). The most critical period of development is during the first trimester, when most women aren’t telling the world they’re pregnant (because it’s also the time when a miscarriage is most likely, and if you do lose the pregnancy you might not want to have to tell everyone). During that period, I found it difficult to explain why I was concerned about the fumes from the roofing adhesive being used in our building. I didn’t want to seem like a princess who thought she was too good to work in conditions that everybody else found acceptable. (After I told them I was pregnant, my coworkers were very understanding about such things.)


Recommendations usually focus on what you should eat during pregnancy, but obviously children’s brain development doesn’t stop there. I’ve opted to take precautions with the food Lily and I eat for as long as I’m nursing her.

Claims that pesticide residues are poisoning children scare me, although most scientists seem to think the paper cited is overblown. Other sources say the levels of pesticides in conventionally grown produce are fine. We buy organic produce at home but eat whatever we’re served elsewhere.

I would love to see a study with families randomly selected to receive organic produce for the first 8 years of the kids’ lives, then looking at IQ and hyperactivity. But no one’s going to do that study because of how expensive 8 years of organic produce would be.
The Biodeterminist’s Guide doesn’t mention PCBs in the section on fish, but fish (particularly farmed salmon) are a major source of these pollutants. They don’t seem to be as bad as mercury, but are neurotoxic. Unfortunately their half-life in the body is around 14 years, so if you have even a vague idea of getting pregnant ever in your life you shouldn’t be eating much farmed salmon (or Atlantic/farmed salmon, bluefish, wild striped bass, white and Atlantic croaker, blackback or winter flounder, summer flounder, or blue crab).

I had the best intentions of eating lots of the right kind of high-omega-3, low-pollutant fish during and after pregnancy. Unfortunately, fish was the only food I developed an aversion to. Now that Lily is eating food on her own, we tried several sources of omega-3 and found that kippered herring was the only success. Lesson: it’s hard to predict what foods kids will eat, so keep trying.
Postscript, 2016: Based on this review, we’ve been giving her a fish-oil supplement which she loves (“More fishy pill!”)

In terms of hassle, I underestimated how long I would be “eating for two” in the sense that anything I put in my body ends up in my child’s body. Counting pre-pregnancy (because mercury has a half-life of around 50 days in the body, so sushi you eat before getting pregnant could still affect your child), pregnancy, breastfeeding, and presuming a second pregnancy, I’ll probably spend about 5 solid years feeding another person via my body, sometimes two children at once. That’s a long time in which you have to consider the effect of every medication, every cup of coffee, every glass of wine on your child. There are hardly any medications considered completely safe during pregnancy and lactation—most things are in Category C, meaning there’s some evidence from animal trials that they may be bad for human children.


Too much fluoride is bad for children’s brains. The CDC recently recommended lowering fluoride levels in municipal water (though apparently because of concerns about tooth discoloration more than neurotoxicity). Around the same time, the American Dental Association began recommending the use of fluoride toothpaste as soon as babies have teeth, rather than waiting until they can rinse and spit.

Cavities are actually a serious problem even in baby teeth, because of the pain and possible infection they cause children. Pulling them messes up the alignment of adult teeth. Drilling on children too young to hold still requires full anesthesia, which is dangerous itself.

But Lily isn’t particularly at risk for cavities. 20% of children get a cavity by age six, and they are disproportionately poor, African-American, and particularly Mexican-American children (presumably because of different diet and less ability to afford dentists). 75% of cavities in children under 5 occur in 8% of the population.

We decided to have Lily brush without toothpaste, avoid juice and other sugary drinks, and see the dentist regularly. We also use a $20 water filter that removes fluoride (we verified with lab tests; I recommend the Maine state lab if you need this kind of thing). Fluoride basically doesn’t pass into breastmilk, but I used it while I was pregnant and will use it when the kids start drinking water instead of mostly milk.

Home pesticides

One of the most commonly applied insecticides makes kids less smart. This isn’t too surprising, given that it kills insects by disabling their nervous system. But it’s not something you can observe on a small scale, so it’s not surprising that the exterminator I talked to brushed off my questions with “I’ve never heard of a problem!”

If you get carpenter ants in your house, you basically have to choose between poisoning them or letting them structurally damage the house. We’ve only seen a few so far, but if the problem progresses, we plan to:

1) remove any rotting wood in the yard where they could be nesting

2) have the perimeter of the building sprayed

3) place gel bait in areas kids can’t access

4) only then spray poison inside the house.

If we have mice we’ll plan to use mechanical traps rather than poison.

Flame retardants

Since the 1970s, California required a high degree of flame-resistance from furniture. This basically meant that US manufacturers sprayed flame retardant chemicals on anything made of polyurethane foam, such as sofas, rug pads, nursing pillows, and baby mattresses.

The law recently changed, due to growing acknowledgement that the carcinogenic and neurotoxic chemicals were more dangerous than the fires they were supposed to be preventing. Even firefighters opposed the use of the flame retardants, because when people die in fires it’s usually from smoke inhalation rather than burns, and firefighters don’t want to breathe the smoke from your toxic sofa (which will eventually catch fire even with the flame retardants).

We’ve opted to use furniture from companies that have stopped using flame retardants (like Ikea and others listed here). Apparently futons are okay if they’re stuffed with cotton rather than foam. We also have some pre-1970s furniture that tested clean for flame retardants. You can get foam samples tested for free.

The main vehicle for children ingesting the flame retardants is that it settles into dust on the floor, and children crawl around in the dust. If you don’t want to get rid of your furniture, frequent damp-mopping would probably help.

The standards for mattresses are so stringent that the chemical sprays aren’t generally used, and instead most mattresses are wrapped in a flame-resistant barrier which apparently isn’t toxic. I contacted the companies that made our mattresses, and they’re fine.

Ratings for chemical safety of children’s car seats here.

Thoughts on IQ

A lot of people, when I start talking like this, say things like “Well, I lived in a house with lead paint/played with mercury/etc. and I’m still alive.” And yes, I played with mercury as a child, and Jeff is still one of the smartest people I know even after getting acute lead poisoning as a child.

But I do wonder if my mind would work a little better without the mercury exposure, and if Jeff would have had an easier time in school without the hyperactivity (a symptom of lead exposure). Given the choice between a brain that works a little better and one that works a little worse, who wouldn’t choose the one that works better?

We’ll never know how an individual’s nervous system might have been different with a different childhood. But we can see population-level effects. The Environmental Protection Agency, for example, is fine with calculating the expected benefit of making coal plants stop releasing mercury by looking at the expected gains in terms of children’s IQ and increased earnings.

Scott writes:

A 15 to 20 point rise in IQ, which is a little more than you get from supplementing iodine in an iodine-deficient region, is associated with half the chance of living in poverty, going to prison, or being on welfare, and with only one-fifth the chance of dropping out of high-school (“associated with” does not mean “causes”).

Salkever concludes that for each lost IQ point, males experience a 1.93% decrease in lifetime earnings and females experience a 3.23% decrease. If Lily would earn about what I do, saving her one IQ point would save her $1600 a year or $64000 over her career. (And that’s not counting the other benefits she and others will reap from her having a better-functioning mind!) I use that for perspective when making decisions. $64000 would buy a lot of the posh prenatal vitamins that actually contain iodine, or organic food, or alternate housing while we’re fixing up the new house.


There are times when Jeff and I prioritize social relationships over protecting Lily from everything that might harm her physical development. It’s awkward to refuse to go to someone’s house because of the chemicals they use, or to refuse to eat food we’re offered. Social interactions are good for children’s development, and we value those as well as physical safety. And there are times when I’ve had to stop being so careful because I was getting paralyzed by anxiety (literally perched in the rocker with the baby trying not to touch anything after my in-laws scraped lead paint off the outside of the house).

But we also prioritize neurological development more than most parents, and we hope that will have good outcomes for Lily.

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34 comments, sorted by Click to highlight new comments since: Today at 11:37 PM

Excelent post! Thanks for sharing.

really good review.

Germs - Good understanding on the hygiene theory. Its worth also adding that younger children get over sickness easier and probably won't have a memory of any pain of the process, so if you were to catch chicken pox - best to do it earlier in life. I personally believe in dirt and other exposure.

Lead - I don't know if you are aware but lead testing kits are pretty easy to acquire. Basic chemistry can help you figure out if a thing is lead or not.

Cats - I would say not to live with cats at all, especially not a small child. I know you think your cats are indoor cats, but a few experiments have been conducted on cats with collar-cameras which showed even the nicest of cats seem to manage to get out and eat things when no one is watching. I wonder if looking into this information will change your mind about the safety of living with cats. Part of me is very concerned about how much we don't know about what toxo does to humans. We know it makes rats more attracted to cats urine to encourage them to get eaten and pass on the toxo. I am concerned for the ability of toxo to get to the brain and modify it.

pets - certainly live with pets, I believe it does wonderful things for social-ness and empathy and companionship. (there is a vegan argument against having animals, but I believe it is important to have them), food animals - i.e. chickens - will help children understand where food comes from, as well as growing foods and herbs, lemon trees, and others add childhood memories to one's life. I personally keep bees, depending on your climate that might not work for you, and also the risk of stings exists. Having a personal model of a creature of a simple mind and simple behaviour is a good thing for building social intelligence brains.

IQ - I have no answer, but there is information that being more than 30 points away from your peers can be socially isolating and not actually lead to progress. If IQ was a good predictor of success (in various metrics) it would be more clear to be so. If you expect the world to change significantly to make this not a problem in the future then carry on, but I don't know how to consider limiting IQ to more socially productive levels.

Good Luck!

Edit: fish - I would trust some fish sources, i.e. river farmed, or private farm - depending on what they feed the fish and where the food comes from. also for the nutrients of fish oils.

One possibility is to get a cat that already has toxoplasmosis (I believe you can get them tested), since they can't shed it after the first few weeks. But you're more likely to get it from undercooked meat, anyway, so if you're really concerned it's probably best to focus attention there.

Source on cats getting out of the house, killing and eating animals, and then sneaking back in unnoticed? Especially unlikely in our second-floor apartment since the cat would have to make it through a closed door four separate times without anyone knowing.

https://en.wikipedia.org/wiki/Cat_behavior suggests that cat behaviour is to escape or try to do so.

some sources of cats damaging wildlife: http://www.telegraph.co.uk/lifestyle/pets/9462354/Cats-killing-more-wildlife-than-previously-thought.html http://www.telegraph.co.uk/lifestyle/pets/9307745/CatCam-could-vindicate-pets-accused-of-killing-birds.html http://www.npr.org/sections/thetwo-way/2013/01/29/170600655/behind-cute-face-a-cold-blooded-killer-study-finds-cats-kill-billions-of-animals

papers: http://www.kittycams.uga.edu/research.html http://www.nature.com/ncomms/journal/v4/n1/full/ncomms2380.html

a fact-check on some information: http://www.abc.net.au/news/2014-11-13/greg-hunt-feral-cat-native-animals-fact-check/5858282 which is hilarious and embarrassing and evidence that chain-of-whispers is very real.

a source that is biased: http://www.australianwildlife.org/media/27964/AWC-Wildlife-Matters-Summer-2012-2013.pdf

a good summary of multiple sides of some studies: http://members.iinet.net.au/~rabbit/catdeb.htm

the basic facts: Cats that are outdoors seem kill a lot of other animals. Sometimes they bring them home, sometimes they do not. Estimates suggest massive 10^6 - 10^9 sort of numbers of animals being killed. If you are sure that your cats never leave the house and never have a chance to eat animals, that's fine, I am still suspicious, what about birds near windows?

-- I have first-hand anec-data about the seriousness of toxoplasmosis.

Having said all this I definitely have a personal preference for liking dogs over cats. As a separate point I prefer the psychology of dogs to that of cats where dogs are happier, and cats are temperamental at times (not counting for variations in both dogs and cats where either can be happy and either can be temperamental)

None of these sources are about indoor cats. They are all about feral or indoor-outdoor cats.

I did find a study about the prevalence of toxo in Polish indoor cats, which was 19% if they were not fed raw meat. A study on "indoor" cats in Rhode Island animal shelters found 26% had toxo. That last one seems a bit odd, because you don't know much about the history of a cat at a shelter. A lot of cat adoption places make you promise to keep the cat indoors, but they have no way of checking, so people returning an unwanted cat to a shelter may claim to have kept their promise even if they didn't. In any case, no indication of whether these cats got toxo while they were indoor cats, or for example while kittens with a different owner.

I would feel more comfortable without cats, but since they belong to my housemates they're not my choice. Luckily one is blind and the other seems pretty incompetent (the cats, not the housemates).

Yes it seems like cats are less bad than I already registered. Most of my argument rests on me also not liking cats. Glad the information has been shared.

Also, there's now a chicken pox vaccine, so no need to catch it at all.


What kinds of pets are third floor apartment friendly? We too have an 1.5 year old girl and would consider a pet when she will old enough to take responsibility for it, like, at 6.We are held back with stuff like cats will fall out a window and disappear. I never had a pet and don't like them much but for example I have seen some apartment kids having turtles, which look like a boring kind of a pet.

Axolotl's are very boring. turtles are interesting if the temperature is above ~25c. often swimming around and eating things. Finches are dumb birds but budgies and larger sized birds are quite smart, have plenty of personality.

I have always found that mice smell.

Stick insects are cool!

Gerbils? Guinea pigs? Mice? Birds? They don't have personality in the way that dogs or cats do, but might appease a six-year-old.

I don't think personality is a necessary trait of a pet. All my sons showed interest in animals large and small to some degree but the second oldest (9) developed a deep interest ina all kinds of animals and knows many more animals and there properties (including typical weight and size) than me or his mother. He observes the animals but doesn't necessariily develop a relationship with them.

The bioterminist's guide is now 5 years old. Does anyone know of an updated version?


The hygiene hypothesis states that lack of exposure to germs and parasites increases risk of auto-immune disease. Our pediatrician recommended letting Lily playing in the dirt for this reason.

It is fairly common-sense where I live - docs say "kids need to eat a kg of dirt a year". The worst thing I did was picking up pigeon feathers from the pavement and licking it. That was actually too much for my immune system, got a streptococcus infection.

We too have a 1.5 year old daughter and it is weird how most things simply don't relate: living in a new build in-situ concrete apartment house, new built = strictly regulated, things like lead or pesticides didn't even come into question. IKEA has always been an obvious choice instead of buying something expensive.

About the child seat in the car, funny story: I was wanting to get rid of my car as it was entirely unnecessary with two tramway lines in front of our flat, but I was in the old "if you have a kid, you must have a car, for emergencies" mood. Well, we had them, as we had this yellow skin / bilirubin issue after birth and went back to the hospital several times, but every time it was far easier to just roll the pram on the comfortably pram and wheelchair accessible tramway and get off 8 stops later than to put the baby seat in the car (we could not leave it there as the sun would make it hot) and then put a sleeping baby in it who will probably wake up and be angry etc. So we got rid of the car soon after. It feels weird, to have a family without a car but I am starting to think it may be the future in such densely settled European metropoles (we live in Vienna). I am worried about my driving skills deteriorating though. Gone are the times when I lived in Birmingham, drove to a client in Edinburgh and wasn't even too tired.

We are not health food types, classic meat and potatoes types more like, so my wife was getting omega-3 from a timed vitamin and supplement complex meant for pregnant women. Timed = different packages for different stages of pregnancy. I have heard some debates about omega-3 pills doing less than actually eating fish, but never really believed them, it is literally fish oil extracts after all. However she likes smoked salmon (IKEA gravadlax) so she ate it occasionally.

Overally so far our results seem genetics based. My daughter is like me in the sense of big, strong, heavy, and lazy, i.e. not wanting to stand and walk at 17 months. This is not strength based, when she gets fussy she kicks like a horse, it is probably laziness based like in my case or poor balance (could also be inherited from me).

She does not speak either and is really fussy, screaming a lot, which is worrisome and stressful, this is a bit unlikely to be genetics (both of us were early talkers and this is usually a sign of intelligence so I am starting to have some fears in the IQ department).

She does not speak either and is really fussy, screaming a lot

Where I live, a child with in that situation would probably be referred for early childhood intervention (a free service where health visitors come to your home and work with you and your child). I wonder if that's available where you live?

For kids that are slow in speaking (or really any babies), one thing that's common here is to use baby sign language to allow them to communicate before they're speaking. We've found it's really helpful for our daughter to be able to communicate things like "more" and "all done" with hand signals. Still working on "hungry" vs. "thirsty", since currently all that is encompassed by "more." I think it reduces fussiness because she can express her needs better and we can meet them better.

Blah. My current fish information factored in mercury but not PCB. I've been thinking atlantic salmon was fine. Now googling "PCB mercury". Is the first result pretty much accurate or is there more to the story? (And any estimates for the magnitude of effect / whether it is worth worrying about?)

I did the same thing. The studies/abstracts I've read talk about effects on children of women with "high levels" of PCBS but I have no idea where I fall on that scale. Like, Inuit women have very high levels, but they're eating very large amounts of fish, seals, etc. This paper has info about health effects of people eating Great Lakes fish, which may be more relevant to you.

My very non-expert impression is that it seems to be less serous than mercury. And even the evidence on mercury had some weird bits, like studies that show mercury is good for babies' neurodevelopment (because they didn't control for maternal fish consumption, and apparently the fish was more helpful than the mercury was harmful!) But obviously the goal is to get the good fish nutrition without the pollutants.

Of course, I live on the great lakes and my family eats a lots of fish... It probably doesn't matter for me but not sure what to feed my little sister now, especially considering what you said about half-life. Attempts at guidelines keep waving around "moderation" in response to mixed messages from research, but even if by coincidence the effects are ∩ shaped and not linear I doubt vague ideas about moderation are going to hit approximately optimal.

Cross fingers and hope the good list is accurate, I guess?

A list of cheaper oily fish with negligible PCBs and mercury

The problem is that fish contamination critically depends on where that fish lived. This means that just a list of fish species isn't very useful, you need to know where that fish was caught and I'm not sure that information is easily available.

Salkever concludes that for each lost IQ point, males experience a 1.93% decrease in lifetime earnings and females experience a 3.23% decrease. If Lily would earn about what I do, saving her one IQ point would save her $1600 a year or $64000 over her career. (And that’s not counting the other benefits she and others will reap from her having a better-functioning mind!) I use that for perspective when making decisions.

This seems horrifically subject to Goodhart's law and confounding. Even if it is true that one IQ point is associated with a $1600 increase in salary, controlling for a variety of confounders, it is not the case that an intervention resulting a one point increase in IQ will have the same effect on salary.

Even if the intervention results in a true increase in IQ of one point that doesn't fade (a problem with many interventions), and even if a perfect analysis was done such that an increase in salary of $1600 was caused by, and not just associated with the one point rise in IQ, it is still not the case that the intervention will result in the same $1600 increase in salary.

By "save" I meant "avoid losing" not "gain an extra." Assuming a child would not normally get mercury poisoning, for example, by preventing mercury exposure I am preventing my child from losing some amount of cognitive ability.

My guess is that interventions like preschool are more likely to fade with time, and brain damage is less likely to fade.

I'm not taking Salkever's numbers literally. But you probably agree that brain damage causes lost value, possibly a lot of lost value. I estimate that I may spend a few thousand dollars on various steps to prevent brain damage to my children. That seems like a good investment to me.

I apologize, I see you clearly brought up IQ in the context of preventing poisoning. That should have a more predictable effect than positive interventions.

Pressure-treated wood is treated with arsenic and chromium. Playing on playsets or decks made of such wood increases children's cancer risk. It should not be used for furniture (I thought this would be obvious, but apparently it wasn't to some of my handyman relatives).

This isn't true in the US at least. The US banned arsenic treated wood for residential use in 2004. I believe the replacement is much safer but I'm not certain.

Thanks; fixed. Our deck is considerably older than that, though, so depending on the wood's age it may still be relevant.

The back deck is ~1993.

The front stairs are ~2008.

Thanks for this. And thanks also for the pointer to Scott's guide.

Did you do any testing pre-pregnancy, i.e. for genetic matchup between you and your husband? And did you do any of the fetal testing mentioned e.g. for autism? Wondering about the cost-benefit on those.

He had testing for a genetic disease done due to his family history. I had whatever the slate of "early risk assessment" treating includes - what I remember is a blood test for cystic fibrosis and an ultrasound to look for signs of Down syndrome. All was covered by insurance. http://www.earlyriskassessment.com/

I'm not aware of prenatal testing for autism? We did both take the Baron-Cohen AQ quiz, which didn't think we were particularly likely to have autistic kids, though I'm not sure that's worth much.

But it’s not something you can observe on a small scale

But you can observe that pyrethrins are used on large scale as food. That is why they are so popular as insecticides. I'll take that thousand year observational study over a single fishing expedition.

People also spent a very long time using lead water pipes and drinking vessels made with lead, and apparently didn't notice a problem.

It doesn't surprise me that ant poison isn't great for children.

No, the Romans were aware of the toxicity of lead.

Yet it was used for water pipes into the 20th century. My understanding is that they knew high doses were toxic, but didn't see a problem with low doses.

But you can observe that pyrethrins are used on large scale as food.

No, you can not. Pyrethrins are basically insoluble in water and people don't eat chrysanthemums from their tea.

I'll take that thousand year observational study

Be careful about that. For example,

The species Aristolochia clematitis was highly regarded as a medicinal plant since the ancient Egyptians, Greeks and Romans, and on to until the Early Modern era; it also plays a role in traditional Chinese medicine.

You actually have more than a thousand years of observational studies, and across different cultures, too. There is only one little problem -- "Aristolochia has been shown to be both a potent carcinogen and kidney toxin."

And I suppose you also deny that there is any cinnamon in cinnamon tea?
In any event, many recipes for insecticide are identical to recipes for chrysanthemum tea.

There is a big difference between food and medicinal doses.

I'm looking to buy a sofa without flame retardants. The Center for Enviromental Health suggests that all IKEA products are fine, but at least in 2012 it seems that they instead substituted another chemical flame retardant, TRIS. Does anyone know if IKEA furniture is now chemical flame retardant free, or if there are any other good options for below $1,000 ?

The law just changed for 2015, so although many companies were switching to less-toxic ones in the past they are now free to not use any flame retardants at all, and some are doing so. All IKEA furniture manufactured after Jan 1, 2015 should be fine. The only exception would be if you somehow bought something that was made before then, but I imagine their turnover is fast enough their 2014 stock is all sold.