Much like the children who have them, baby teeth are tiny, delicate, and undeniably weird. Otherwise known as primary teeth, kids sell baby teeth to an imaginary fairy and parents store them in sentimental boxes. But that’s just the tip of the canine when it comes to how odd baby teeth truly are — and the science, from teething to adulthood, gets stranger from there. But perhaps the most important thing baby teeth have in common with kids is that well-intended parents can screw them up very easily.

Here are nine weird scientific facts about baby teeth all parents should now.

Baby Teeth Grow in the Womb

Your kid’s teeth are one of the first things they’ll ever grow. Baby teeth form in the womb as early as six weeks into pregnancy. During this time, a section of tissue known as the dental lamina begins to grow along the gum line, where sections of cells known as tooth buds begin to grow. At about three to four months of pregnancy, fetuses start to form hard tissue around their teeth, which typically stay below the surface until babies are born and are about six months old.

So as strange as it may sound, babies technically have their first set of pearly whites before they meet their parents. This can get especially weird when one twin absorbs the other, because the teeth can turn up inside of the surviving fetus’s body later in life — the ultimate passive-aggressive sibling move.

Baby Teeth Are Essential Placeholders

Although baby teeth do not seem to serve much of a purpose as much as they are a nuisance, they are important placeholders in children’s growing jaws. That’s why in spite of their small size, baby teeth are a big deal.

“As children, our jaws are not fully formed yet, so there isn’t enough space for a full set of adult teeth,” says dentist Mike Golpa, D.D.S. “The jaw bone can deteriorate or change, however, without the teeth there, so baby teeth act as stand-ins until adult teeth are ready to come in.”

Even though kids will eventually lose them (like anything else they’re expected to hang onto), baby teeth are incredibly consequential, and there are plenty of things that can go wrong with them. For instance…

Some Babies Are Born With Teeth Already

“Some babies may be born with one or more teeth,” says Namrita Harchandani, D.D.S, a dentist from AuthorityDental.org. Known as natal teeth, this occurs in about one in every 2,000 babies. These teeth may be yellow or brown, and tend to be looser and easier to dislodge than other baby teeth because the root is not fully developed. This poses a choking hazard, so doctors may remove these teeth to alleviate the risk.

Some Babies Grow Teeth Too Early

While natal teeth are chompers that show up at birth, neonatal teeth are ones that sprout within their first month of life. These are typically infants’ front bottom teeth, otherwise known as their mandibular incisors. This is not as common as babies who are born with teeth, but the problems are similarly related to them being too loose. Depending on how loose, doctors may remove them to avoid the risk of aspiration or ingestion. However, losing baby teeth too early could cause adult teeth to grow in crowded and crooked, so if they are not too loose, doctors may leave the teeth in. This may come as unfortunate news to breastfeeding mothers, but many babies are able to adjust and eat without biting.

Healthy Baby Teeth Are Blue

When healthy baby teeth erupt within an infant’s first six months, they manage to stay creepy. Baby teeth come in a slightly different color than permanent teeth. It’s not the sleep deprivation talking, and your eyes are not playing tricks on you. “Baby teeth are bluish-white in color and brighter than permanent teeth,” Harchandani notes.

Some Babies Have More Than 20 Teeth

Most babies are born with 20 tooth buds that form 20 baby teeth, but occasionally kids may have more than 20 baby teeth, a condition known as hyperdontia. Hyperdontia occurs when extra teeth pop up, often behind the bottom front teeth. This occurs with permanent teeth as well, but it is more common in baby teeth. Scientists suspect it’s a result of growing tooth bud cells splitting off into separate cells. More often than not, doctors will remove extra baby teeth to make room for permanent teeth to grow in.

Some Baby Teeth Get Stuck

In some instances, baby teeth can fuse to the surrounding bone, which causes them to sink into the nearby gum tissue, the National Institutes of Health explains, causing what dentists call dental ankylosis. This can happen to adults as well, but it is 10 times more common with baby teeth.

For most children, small fibers hold baby teeth in separate sockets, but with ankylosis, baby teeth attach to the nearby bone instead. This condition is not always obvious until children fail to lose their baby teeth, which is why some adults still have their baby teeth. This may be great for the Tooth Fairy’s budget (which has inflated over the years), but is bad news for permanent teeth, which won’t have room to grow unless ankylosed teeth are removed.

Baby Teeth Get Are Full of Cavities and “Nursing Caries”

Like the children who have them, baby teeth are small, delicate, and easily spoiled rotten. Tooth decay, also referred to as dental caries or cavities, is the most common chronic illness among young children. Data indicates about 42% of children aged 2 to 11 have had at least one cavity in their baby teeth. This high incidence is only partially explained by kids’ increased likelihood of consuming sugar and starches, which cause dental caries, and decreased likelihood of practicing proper oral hygiene, compared to adults.

Babies are born without the bacteria mutans streptococcus, which causes cavities, in their mouths, but they become infected from sharing utensils and food with their parents usually before the age of 2. Families tend to share the same composition of bacteria from living in the same environment, eating the same foods, and physically interacting with one another. This is why parents who’ve had more cavities are more likely to have kids with cavities — not because they have “soft teeth.”

It is important to note that infants are also more likely to get what’s called “nursing caries” from drinking a bottle at night in their crib, a habit that is discouraged by pediatricians and dentists alike because it exposes vulnerable teeth to sugar in milk and formula for longer periods of time.

Baby Teeth Might Give Clues Clues About When to Wean

Similar to bottle feeding at night, there is evidence that breastfeeding after 12 months could lead to cavities in babies as well, though breastmilk in itself does not appear to be the cause. Rather, studies suggest that nighttime feedings on-demand after teeth have started to grow in increases the risk of cavities because it’s more difficult to maintain oral hygiene with a fussy infant in the middle of the night compared to daytime feedings. Still, rather than recommended parents deny their children breastmilk, dentists and pediatricians simply recommend to brush with a fluoride toothpaste afterward.

In contrast, anthropologists believe that ancient baby teeth fossils show signs of stress from weaning too soon, which could have contributed to malnutrition, disease, and shorter lifespans. So no matter what parents decided to do when it comes to breastfeeding, it’s going to show up on babies’ creepy teeth. But if breast is best for your kid, just don’t forget their toothbrush.

This article was originally published on Oct. 24, 2019