How much should you protect your child?

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.


4 thoughts on “How much should you protect your child?

  1. kernly

    I suspect your efforts are misguided. First of all, you’re worrying about imperceptible problems when perceptible problems are going to arrive. Your kid is gonna get banged on the head hard enough to raise a bump. Your kid is gonna get sick, sick enough to keep her in bed for a while. Your kid is gonna be exposed to enough smoke and particulate matter to make her cough and choke. The world’s gonna give her knocks that are completely incomparable with eating a little pesticide on an apple or being exposed to a little bit of lead, once. What you’re doing might be like worrying about a few potential scratches on a car that’s certainly gonna get hit with a hammer a few times, and possibly be entered into a demolition derby.

    Second of all, do you actually know enough about the class of potential imperceptible problematic things to usefully deal with them? As far as mercury goes, “playing with mercury” isn’t a huge deal, compared to eating too much fish. Fish accumulate methylmercury, which is very very very bad. Elemental mercury, on the other hand, you can drink with pretty much no problem. That’s not to say elemental mercury is fine, the *fumes* from it aren’t, but it is not as threatening as other varieties. Which exist in significant quantities in your can of tuna.

    Buying organic produce doesn’t sound like a good move. “Organic” farms have to do pest/disease control somehow, and that’s probably higher risk than using normal pesticides. There are tests for whether things are “carcinogenic” – for example, take some bacterial cultures and expose them to some potential carcinogen, then to some toxin normally kills that bacteria. The proportion of survivors increases if the substance caused mutations/was carcinogenic. They tested pesticides, and found carcinogens. But plants in general trip that test. Crops that are bred for a pesticide free environment actually score higher on this test, which shouldn’t be surprising – *something* has to stop those plants from getting eaten, and that something is some kind of poison. Eliminating pesticides is probably just exchanging a known, efficiently delivered poison mostly on the surface for permeating, unknown, relatively inefficient poisons. Not that it’s something to be terrified of, we evolved to deal with a certain amount of chemical deterrence. But when the price for the latter is much higher, the whole business seems terribly silly. That’s putting it charitably.

    I don’t know enough to criticize the other stuff you raise, but I suspect that there are similar misunderstandings lurking there, too. I think you’re trying hard to prevent the potential derby car from getting scratched, and in addition you don’t actually know how to prevent the small fraction of scratches that you’ve been made aware of, which are themselves a small fraction of the scratches that will inevitably arrive. You could make a full time job of trying to figure out what we really know about preventing scratches, and it wouldn’t add up to preventing a dent – or even to preventing most scratches!

    The problem I have is that this effort and attention could be spent on things that will actually protect the child. Savings can confer real protection. More money equals more security and more options. You talked about your kid’s potential future income – well, that’s great, but it’s *potential.* Real money in the bank is better. God knows what will happen to your kid over her lifetime. Cancer is likely, at some point. Good doctors cost money. And what about things that will happen to *you*? What if you and/or your husband lose your jobs? Get sick? Whether it happens before or after your child leaves the nest, it will probably affect her, and if finances are a concern that multiplies the difficulty. This is a very significant threat, and more importantly an addressable one. I’m not telling you to be anxious – I’m telling you, if you’re anxious, this is something that can actually help when things go wrong. If you’re gonna channel your anxiety into action, channel it usefully. For bonus points, teach your kid to do the same when she gets old enough.

    Lack of money is probably the biggest addressable threat, but there are others. Lifestyle issues are probably more gene-driven than most people would ever imagine, but there’s certainly an environmental aspect. It can’t be bad to start your kid off eating not too little, and not too much. Exercising not too little, or too much. Both extremes are easily achievable, but there’s also a big sweet spot where you’re doing just fine. Cars kill lots of people, but a good car can confer real protection. It’s probably a good idea to optimize your tires, too – snow tires for winter, summer tires for summer. That’s a big improvement on handling compared to all-season tires, and being in control of your car can be very important. Buy wheels for the tire changes, you can change wheels out yourself, you can’t change the tires themselves yourself.

    Good luck to you and Lily! She’ll probably do OK – however much effort you put into optimizing your parenting.

  2. Julia Wise

    I agree that it’s inevitable that bad things will happen to Lily. I don’t think that means we should throw up our hands and say, “No point in trying to prevent anything.” It’s one thing to accept that your car will get dents, but another to do nothing while the neighbor throws rocks at it. Also, things are cumulative. Exposure to one danger and exposure to another danger is *more dangerous* than either independently. It’s not as if children are either in pristine condition or damaged goods – there’s a gradient in between.

    (That said, I keep a mental list of smart people I know and the head injuries they got as children, so I can remind myself that when Lily inevitably gets one it doesn’t spell doom.)

    I’m not sure how you conclude from anything I’ve written that I think mercury in fish is not a problem. As I said, we don’t eat fish that are high in mercury.

    I’m also aware that cars are one of the most likely things to kill children, which is part of why we don’t own one.

    Thank you for your concern about our financial situation, but we’re really doing fine. We’re unfortunately all too aware of what cancer costs and will be as equipped as anyone to handle it if/when needed.

    1. kernly

      “It’s one thing to accept that your car will get dents, but another to do nothing while the neighbor throws rocks at it.”

      For sure! And it’s one thing to do something that deals with a clear and present issue (“Hey! Stop throwing rocks at my car!”) and quite another to spend effort trying to head off potential, as yet unrealized sources of damage (putting up a sign saying “no throwing rocks at my car!” when no-one has.) And it’s one thing to get super mad about someone throwing rocks at your car and take action (call the police) and another to get super mad about being dinged and take similar action. If you make either kind of error, grossly miscalculating the probability that various kinds of danger will arrive, or grossly miscalculating the threat that those things pose, then your efforts are almost sure to be wasted.

      “I’m not sure how you conclude from anything I’ve written that I think mercury in fish is not a problem”

      It just seemed odd that to mention “playing with mercury” as something that potentially caused you significant harm, if you know about the various forms mercury takes and the very different threats those different forms pose to people. I didn’t see you mention avoiding fish – my mistake.

      “Thank you for your concern about our financial situation, but we’re really doing fine”

      If you’re millionaires my advice would still apply. More savings is always safer, and in the absence of clear and present threats to be dealt with it’s always gonna be a great way to improve security. Indeed it’s silly to just pour money into a savings account after a certain point – you diversify, buy some hard assets, maybe set up accounts and properties abroad, etc. You can always become more financially secure. And financial ruin has struck many who had good reason to think they would never have to worry about money again.

      I would honestly compare financial ruin with cancer – an ever-present, terrible threat hovering over everyone. But unlike with cancer, you can take steps so you (and your family!) become much less vulnerable to it. It’s true that some risk factors mean you’re at much greater risk, but it can never ever be disregarded.

  3. Julia Padua Whiteneck

    I think it is hard to be a smart parent – my girls still make me wake at night in near-terror at their possible futures (they are 22 and 24). The more you know, the scarier the world is! The hardest part about being a parent at all, though, is that although we are all in this together, we all make our own decisions about what is best for children.



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