Commonly used baby soaps and shampoos, including products from Johnson & Johnson, Aveeno and CVS, can trigger a positive result on newborns' marijuana screening tests, according to a recent study. A minute amount of the cleansing products in a urine sample — just 0.1 milliliters or less — was found to cause a positive result.
Researchers at the University of North Carolina, Chapel Hill, began studying the issue after an unusually high number of newborns in their nursery began testing positive for marijuana exposure. Newborn screening for marijuana at hospitals, particularly among babies of women who are considered at high risk of drug use, is not uncommon: at U.N.C. Chapel Hill, 10% to 40% of newborns are tested.
Positive results can precipitate an investigation by child welfare authorities. "We really did this to help protect families from being falsely accused," study co-author Dr. Carl Seashore, a pediatrician in the U.N.C. Chapel Hill newborn nursery, told My Health News Daily.
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Soaps that were specifically associated with false-positive marijuana test results include Johnson & Johnson’s Bedtime Bath, CVS Night-Time Baby Bath, Aveeno Baby Soothing Relief Creamy Wash and Aveeno Baby Wash & Shampoo.
Other products, such as Johnson’s Head-to-Toe Baby Wash, CVS Baby Wash, Baby Magic and even standard hospital gel hand soap, also indicated the presence of marijuana metabolites when tested, but not at sufficient levels to qualify as a positive result according to the hospital lab's standards.
The problem is almost certainly not limited to these products, however. Researchers also tested ingredients used widely in soaps and shampoos, including polyquaternium-11 and cocamidopropyl betaine, which both elicited positive marijuana test results. So far, there is no explanation as to why the chemicals interfere with the test's function, but importantly, they aren't intoxicating; they don't cause symptoms of marijuana exposure in children. The researchers think minute amounts of the substances were simply washing off the babies' skin into their urine samples and confounding the screens.
While more sophisticated and expensive testing can easily distinguish between true and false positive results, most hospitals don't use such tests because of the time and costs involved. And positive tests found at the hospital aren't typically sent to outside labs for confirmation, which makes false positive results — and possible investigations afterward — all the more troubling.
Indeed, why hospitals test infants for marijuana exposure in the first place is not entirely clear. Twelve U.S. states designate prenatal exposure to any illegal drug as child abuse; however, there is no scientific evidence that connects marijuana-smoking by a parent with abuse.
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The question is not whether it's acceptable for expectant mothers to use illegal drugs. No child-health expert would characterize recreational drug use during pregnancy as a good idea. But it's not at all clear that the benefits, if any, of newborn marijuana screening — particularly given how selectively the tests are administered — justify the potential harm it can cause to families.
“If the issue is that the mother broke the law and therefore the child should be removed, we might want to consider going after mothers who exceed the speed limit while driving," says Carl Hart, an associate professor of psychology at Columbia University and author of a leading text on drug effects. "Of course, this is ridiculous.” (Full disclosure: Hart and I are currently collaborating on a book project.)
To remove children from their home at birth because of a positive marijuana test is immediately and inexorably harmful, says Richard Wexler, executive director of the National Coalition for Child Protection Reform. "Even when the test is accurate, there is no evidence that smoking pot endangers children," he says, adding, "There is overwhelming evidence that needless foster care endangers children.”
Wexler explains that the odds of abuse and neglect are higher in foster care than they would be at home for the babies. “These infants are being taken from homes where there is no evidence of abuse, and placed in a situation where the odds of abuse are at least 1 in 4,” he says. "The odds of this kind of separation doing emotional damage are nearly 100%. Children risk enormous emotional trauma when they are torn from their mothers during a crucial period for infant-parent bonding.”
One study of infants who were exposed to cocaine in the womb found that their physical growth and development increased when they remained with their biological mothers, compared with being removed from the home because of maternal drug use. “For the foster children, being taken from their mothers was more toxic than the cocaine,” Wexler says.
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The effects of prenatal drug exposure can vary widely. Maternal cocaine use during pregnancy has been linked with subtle developmental problems in children. But despite the popularized notion of permanently disabled "crack babies," the research shows that the harms of cocaine use in pregnancy are on par with those associated with smoking cigarettes. Both can increase the risk of preterm birth and stillbirth. Neither is as dangerous as alcohol, which can cause irreversible intellectual disability.
The evidence on marijuana is inconclusive: Some studies link marijuana use in pregnancy with reduced fetal growth and behavioral problems, but other research has found no effect. Again, the science shows no damage that approaches the harm linked with alcohol or cigarettes.
Although marijuana exposure has not been associated definitively with child harm, testing for it and placing children in foster care unnecessarily has been. Worse, the risks of custody loss are not applied equally to all women.
Determining whether a mother is considered at high risk for drug use — and warrants newborn testing — is ostensibly based on objective factors like whether she failed to obtain prenatal care or has acknowledged being a drug user. But in reality, characteristics like race often dictate which women are singled out for testing: a 2007 study found that babies born to black mothers were 50% more likely to be tested than white infants, even though rates of drug use and odds of positive results didn't vary by race.
If you now consider the additional risks of false-positive results due to bath soaps, it’s hard to make the case for continued newborn marijuana testing — especially if the ultimate goal is to help children thrive.
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Maia Szalavitz is a health writer for TIME.com. Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland's Facebook page and on Twitter at @TIMEHealthland.