Why Are My Child’s Teeth Turning Black?

Why Are My Child’s Teeth Turning Black? Let’s Talk About Chromogenic Bacteria

As a pediatric dentist, one of the most common questions I hear from parents is:
“Why does my child have black stains on their teeth even though they brush every day?”

I know how surprising — and sometimes alarming — it can be to see those dark lines or dots along your child’s gumline. But the good news is: in most cases, those stains are completely harmless and relatively easy to manage.

Let’s dive into what’s really going on — and how we can help.

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What Are These Black Stains?

Those dark markings you see are usually caused by something called chromogenic bacteria. These naturally occurring bacteria produce pigments that react with iron in your child’s saliva, creating a black or dark brown stain, typically along the gumline of their molars or front teeth.

These stains are called extrinsic, meaning they’re on the outside of the teeth. They don’t damage the tooth itself, and they’re not a sign of cavities or poor brushing. In fact, some studies show kids with this kind of stain may even have a lower risk of cavities due to the makeup of their oral bacteria.

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What Causes These Stains?

While the bacteria are the root cause, a few factors can increase the likelihood of staining:

1. Diet

Foods and drinks rich in dark pigments — like blueberries, blackberries, grape juice, soy sauce, or tomato-based sauces — can all contribute. These pigments stick to the bacteria on the teeth and deepen the stain over time.

2. Iron Supplements

If your child takes iron (especially in liquid form), this can increase iron levels in their saliva, giving the bacteria more to work with. This often leads to more prominent dark stains.

3. Swimming in Chlorinated Pools

Kids who spend a lot of time swimming — especially in pools where the pH isn’t properly balanced — may experience slight enamel changes. This can make the teeth more porous and more likely to collect stains. This condition is sometimes called “swimmer’s calculus.”

4. Saliva & Oral Bacteria

Some children naturally have a different balance of bacteria and saliva chemistry. A more alkaline pH or higher calcium in their saliva can create the perfect environment for chromogenic bacteria to thrive. This isn’t something they’re doing “wrong” — it’s just their biology.

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What Do These Stains Look Like?

Black stains from chromogenic bacteria usually appear as thin, dark lines along the gumline. They’re often found on the inside (tongue side) of the molars and front teeth. They’re hard, not sticky, and don’t come off with regular brushing — which can be frustrating for parents. But rest assured, they are cosmetic and not a sign of dental disease.

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How Do We Treat and Prevent Them?

In the Office:

The simplest solution? A professional cleaning. During your child’s routine visit, we can polish away these stains safely and gently. Most kids leave with their teeth looking bright and clean again.

At Home:

There are a few things you can do between visits to help keep stains from coming back:

• Encourage twice daily brushing and flossing with fluoride toothpaste. Electric toothbrushes can also help keep staining to a minimum.
• Have your child rinse with water after eating berries or drinking dark juices.
• If your child takes iron, ask your pediatrician or dentist if there’s a chewable or less staining alternative.
• For swimmers, a quick rinse after getting out of the pool can help.
• Keep up with regular dental checkups — we’ll keep an eye on it for you!

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A Final Word for Parents

Black stains from chromogenic bacteria are extremely common, especially in children — and they’re nothing to be embarrassed about. They don’t mean your child isn’t brushing well, and they don’t mean cavities are forming. In fact, many kids outgrow these stains as their adult teeth come in and their oral microbiome changes.

So if you’re seeing these stains, don’t worry — you’re not alone, and we’re here to help. If you’re in the Novato area and have questions about stains on your child’s teeth, reach out to us at Poppy Kids Pediatric Dentistry. We’d love to help your child smile confidently again!

-Dr.Andrea