If you're the parent of young kids, think about how big a grain of rice is, or a pea, before you help them brush their teeth. That's because that's how big the drop of toothpaste on their toothbrush should be, depending on their age—kids up to age 3 get the rice-sized dollop, kids 3 to 6 get the pea—or they risk developing white streaks or lines on their teeth from a condition known as dental fluorosis, the New York Times reports. The CDC takes claim for this warning after its latest study, based on data from 2013 to 2016 on 5,157 kids between the ages of 3 and 15, found that young children are using too much toothpaste and swallowing too much of it, which also means they're swallowing the fluoride in it. Almost 40% of children between the ages of 3 and 6 are using toothpaste to excess, per the study.
The American Dental Association notes the excess fluoride only affects emerging teeth, which is why only kids get the telltale white spots on their chompers. Confusing parents is that the CDC's suggestion for when kids should start using fluoride toothpaste is at odds with the ADA and the American Academy of Pediatric Dentistry: The CDC says to wait until kids turn 2, while the two dental groups say a small amount of fluoride toothpaste can be used as soon as teeth start to poke out, which can be as soon as a baby is 6 months old. However, Alene Marie D'Alesio, the Children's Hospital of Pittsburgh's pediatric dentistry chief, says much of the trouble can be avoided by parents simply standing over their kids' shoulders while they brush. The ADA notes that, besides the faint white marks on kids' teeth, fluorosis doesn't adversely affect tooth health or function and may actually help fend off tooth decay. (Read more discoveries stories.)