That's the question many health experts are asking as they seek to understand the cause and potential treatment options for a disease that is so preventable, yet continues to plague more children each year.

According to the Centers for Disease Control and Prevention, tooth decay is one of the most common diseases affecting America's children. It's five times more common than asthma and seven times more common than allergies.

Despite simple prevention methods, 42 percent of kids aged 2 to 11 have had cavities in baby teeth while 21 percent of kids aged 6 to 11 have cavities in their permanent teeth.

Researchers think it's due to a combination of several factors including family history, lack of parental awareness, and an overall increase in the amount of sugar kids consume each day.

Cavities, or dental caries, are actually caused by a group of germs called mutans streptococcus. These germs feed on sugar and produce an acid that eats away at the enamel of the teeth. They also produce plaque — the sticky yellowish film that builds up on teeth and damages the enamel.

These bacteria are easily spread within families — every time you share a drink with your kids or eat from the same fork. So parents who had a lot of cavities as kids likely have more of these germs in their mouths and are therefore more likely to spread them to their kids. That explains why some kids can eat lots of candy and never floss but still remain cavity-free while others have cavities even after following good dental hygiene practices and eschewing sugar.

Most parents don't know that cavities are caused by germs nor do they realize that they could be spreading these germs to their kids. So they take their time about their getting their kids in to see a dentist. Both the American Academy of Pediatricians and the American Academy of Pediatric Dentists suggest that babies see a dentist before their first birthday. But studies show that only 10 percent of 1-year-olds and 24 percent of 2-year-olds had been to the dentist. After age two, those cavities are well underway.

Finally, there's the sugar issue. Limiting sugar is one of the best ways to prevent cavities. And that's not just candy bars and sodas. Most parents don't realize that starchy foods such as crackers and cereal also promote tooth decay. Drinks — including fruit juices, formula, and even breast milk — also contain sugars and should not be allowed to sit on a child's teeth. Dentists are still seeing an increase in what they call "baby bottle tooth decay" in young kids who are allowed to sleep with a bottle that is filled with formula or juice. Prompt brushing after meals and sticking with water in between meals can help to reduce cavities.

Bottom line: From the moment your baby's first tooth erupts through the gums, it is susceptible to tooth decay. But there are lots of things that you can do — such as limiting sugar, cleaning your child's teeth, and making that first dental appointment — that can help to prevent cavities and protect your baby's smile for years to come.