Corrections & clarifications: This story has been updated to reflect the age at which the American Academy of Pediatrics recommends parents should brush their children's teeth.

Children are brushing their teeth with so much toothpaste that it's unhealthy, the Centers for Disease Control and Prevention says.

Nearly 40 percent of kids ages 3 to 6 use more toothpaste than recommended by dentists, a CDC study found. The CDC and the American Dental Association recommend that children in that age group should use no more than a pea-size amount of paste. Children younger than 3 should use only a smear, only the size of a rice grain.

The CDC findings released Friday were based on a survey of parents with children ages 3 to 15, and it found about 60 percent of children and teens 3 to 15 used a half or full load of toothpaste. In children 3 to 6, about 12 percent used a smear, 49.2 percent used a pea-size amount, 20.6 percent used a half load and 17.8 percent used a full load.

Brushing with too much toothpaste can damage enamel, because children could swallow too much fluoride while their teeth are developing, the CDC says. That can cause dental fluorosis, white marks and discoloration of teeth.

Brushing habits of about 5,100 children were included in the report based on data from 2013 to 2016.

The American Academy of Pediatrics recommends baby teeth are brushed with a smear of fluoride toothpaste as soon as teeth erupt. The CDC survey found that nearly 80 percent of children began brushing after 1 year.

The data used for the analysis was based on parents' self-reporting. Also, it is unknown whether the toothpaste reported was fluoride or non-fluoride.

More:You're probably brushing your teeth with fecal matter

More:What would happen if you didn’t brush your teeth for a year?

Follow Ashley May on Twitter: @AshleyMayTweets