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 A new study that analyzed other studies (a meta-analysis) found that the class of flame retardant chemicals called PBDEs (commonly found in furniture and household products) has an effect on children's intelligence, so that it results in a loss of IQ points. Most of the studies looked at the child's exposure to flame retardants during pregnancy and then later IQ. They found that the child's IQ was reduced by 3.70 points for each ten-fold increase in flame retardant levels (thus, the higher the PBDE levels, the greater the effect on the child's IQ). This is of concern because flame retardants are in so many products around us, both in and out of the home. Older flame retardants (PBDEs) were phased out by 2013, but it turns out that the newer replacements (TBB and TBPH, including Firemaster 550) also get into people and also have negative health effects.

More and more research is finding health problems with flame retardants because they are "not chemically bound" to the products in which they are used - thus they escape over time. and get into us via the skin (dermal), inhalation (from dust), and ingestion (from certain foods and dust on our fingers). And because flame retardants are persistant, they bioaccumulate (they build up over time). They can be measured in our urine and blood. Evidence suggests that flame retardants may be endocrine disruptors, carcinogenic, alter hormone levels, decrease semen quality in men, thyoid disruptors, and act as developmental neurotoxicants (when developing fetus is exposed during pregnancy)  so that children have lowered IQ and more hyperactivity behaviors.

Where are flame retardants found? All around us, and in us. They are so hard to avoid because they're in electronic goods, in upholstered furniture, polyurethane foam, carpet pads, some textiles, the foam in baby items (car seats, bumpers, crib mattresses, strollers,nursing pillows, etc.), house dust, building insulation, and on and on. What to do? Wash hands before eating. Try to use a vacuum cleaner with a HEPA filter. Try to avoid products that say they contain "flame retardants". Only buy upholstered furniture with tags that say they are flame retardant free. The California Childcare Health Program has an information sheet on how to lower exposure to fire retardants. From Medical Xpress:

Flame retardant exposure found to lower IQ in children

A hazardous class of flame retardant chemicals commonly found in furniture and household products damages children's intelligence, resulting in loss of IQ points, according to a new study by UC San Francisco researchers. The study, published Aug. 3, 2017, in Environmental Health Perspectives, included the largest meta-analysis performed on flame retardants to date, and presented strong evidence of polybrominated diphenyl ethers' (PBDE) effect on children's intelligenceDespite a series of bans and phase-outs, nearly everyone is still exposed to PBDE flame retardants, and children are at the most risk," said UCSF's Tracey Woodruff, professor in the Department of Obstetrics, Gynecology and Reproductive Sciences..... 

The findings go beyond merely showing a strong correlation: using rigorous epidemiological criteria, the authors considered factors like strength and consistency of the evidence to establish that there was "sufficient evidence" supporting the link between PBDE exposure and intelligence outcomes. Furthermore, a recent report by the National Academies of Sciences endorsed the study and integrated evidence from animal studies to reach similar conclusions that PBDEs are a "presumed hazard" to intelligence in humans.

Researchers examined data from studies around the world, covering nearly 3,000 mother-child pairs. They discovered that every 10-fold increase in a mom's PBDE levels led to a drop of 3.7 IQ points in her child." "Many people are exposed to high levels of PBDEs, and the more PBDEs a pregnant woman is exposed to, the lower her child's IQ," said Woodruff. "And when the effects of PBDEs are combined with those of other toxic chemicals such as from building products or pesticides, the result is a serious chemical cocktail that our current environmental regulations simply don't account for." The researchers also found some evidence of a link between PDBE exposures and attention deficit hyperactivity disorder (ADHD), but concluded that more studies are necessary to better characterize the relationship.

PBDEs first came into widespread use after California passed fire safety standards for furniture and certain other products in 1975. Thanks to the size of the Californian market, flame retardants soon became a standard treatment for furniture sold across the country..... Mounting evidence of PDBEs' danger prompted reconsideration and starting in 2003 California, other states, and international bodies approved bans or phase outs for some of the most common PBDEs. PBDEs and similar flame retardants are especially concerning because they aren't chemically bonded to the foams they protect. Instead, they are merely mixed in, so can easily leach out from the foam and into house dust, food, and eventually, our bodies. [Original study.]

This research finding of lower IQ in children with higher exposure to 2 common phthalates during pregnancy is very troubling. Especially since avoiding all phthalates in the USA is currently impossible. But one can lower levels in the body by reading all ingredients and trying to avoid certain products (e.g. dryer sheets, vinyl shower curtains, personal care products with phthalates, scented products). And don't microwave food in plastic containers. From Science Daily:

Prenatal exposure to common household chemicals linked with substantial drop in child IQ

Children exposed during pregnancy to elevated levels of two common chemicals found in the home -- di-n-butyl phthalate and di-isobutyl phthalate -- had an IQ score, on average, more than six points lower than children exposed at lower levels, according to researchers.

DnBP and DiBP are found in a wide variety of consumer products, from dryer sheets to vinyl fabrics to personal care products like lipstick, hairspray, and nail polish, even some soaps. Since 2009, several phthalates have been banned from children's toys and other childcare articles in the United States. 

Researchers followed 328 New York City women and their children from low-income communities. They assessed the women's exposure to four phthalates--DnBP, DiBP, di-2-ethylhexyl phthalate, and diethyl phthalate--in the third trimester of pregnancy by measuring levels of the chemicals' metabolites in urine. Children were given IQ tests at age 7.

Children of mothers exposed during pregnancy to the highest 25 percent of concentrations of DnBP and DiBP had IQs 6.6 and 7.6 points lower, respectively, than children of mothers exposed to the lowest 25 percent of concentrations after controlling for factors like maternal IQ, maternal education, and quality of the home environment that are known to influence child IQ scores. The association was also seen for specific aspects of IQ, such as perceptual reasoning, working memory, and processing speed. The researchers found no associations between the other two phthalates and child IQ. The range of phthalate metabolite exposures measured in the mothers was not unusual: it was within what the Centers for Disease Control and Prevention observed in a national sample.

"A six- or seven-point decline in IQ may have substantial consequences for academic achievement and occupational potential.""While there has been some regulation to ban phthalates from toys of young children," adds Dr. Factor-Litvak, "there is no legislation governing exposure during pregnancy, which is likely the most sensitive period for brain development. Indeed, phthalates are not required to be on product labeling."

While avoiding all phthalates in the United States is for now impossible, the researchers recommend that pregnant women take steps to limit exposure by not microwaving food in plastics, avoiding scented products as much as possible, including air fresheners, and dryer sheets, and not using recyclable plastics labeled as 3, 6, or 7.

The findings build on earlier, similar observations by the researchers of associations between prenatal exposure to DnBP and DiBP and children's cognitive and motor development and behavior at age 3. This September, they reported a link between prenatal exposure to phthalates and risk for childhood asthma. It's not known how phthalates affect child health. However, numerous studies show that they disrupt the actions of hormones, including testosterone and thyroid hormone. Inflammation and oxidative stress may also play a role.