Ashton Kutcher and Mila Kunis say they don't bathe their kids every day - and a pediatrician says they're on to something

• Ashton Kutcher and Mila Kunis sparked a conversation by saying they don't bathe their kids daily.
• A pediatrician said that kids need baths only when dirty, or at least once a week.
• If a daily bath routine works for your family, you should use plain water and skip the bubble bath.

Ashton Kutcher and Mila Kunis recently shared a dirty little secret: They don't bathe their children every day, and limit soap for themselves.

While it might be a headline-grabbing admission, a pediatrician who spoke with Insider said that the A-list couple is on to something.

"Our body makes natural oils to protect our hair and skin," said Daniel Ganjian, a pediatrician at Providence Saint John's Health Center in Santa Monica, California. "It's good to keep those natural oils going."

How often you should bathe your kids depends on how dirty they are

Just how often you should bathe or shower your children depends on their age and how messy they are, Ganjian said. The American Academy of Dermatology Association recommends that babies be bathed twice weekly, while older kids get a bath at least once a week.

Speaking on Dax Shepard's podcast, "Armchair Expert,'' Kunis said that she's never been a stickler for bath time.

"I didn't have hot water growing up as a child, so I didn't shower much anyway," Kunis said. "But when I had children, I also didn't wash them every day. Like, I wasn't the parent that bathed my newborns - ever."

Kutcher summed it up more bluntly, saying that the couple's children - Wyatt, age 6, and Dimitri, 4 - get baths only when necessary.

"Now, here's the thing: If you can see the dirt on them, clean them. Otherwise, there's no point."

Ganjian told Insider that's a reasonable approach, especially for younger kids.

"Typically, as adults, we take daily showers because of smell and body odor, but small kids don't have that smell and body odor," he said. Usually, body odor hits when kids start entering puberty, about age 10, Ganjian said.

If your child loves daily baths, skipping soap or bubbles is recommended

Although daily baths for the younger set aren't necessary, Ganjian recognizes that baths are an important part of the bedtime routine in many families. If your children are soothed by time in the water, baths can be a great way to transition them to bed. Ganjian recommends the four B's bedtime routine - bath, brush, book, bed - but said the first B isn't always necessary.

If you're going to give your kids baths daily, Ganjian recommends skipping soap and shampoo except for once a week. Using those daily can strip natural oils and leave kids' skin feeling dry or irritated. This is especially important for children predisposed to allergies and eczema. Ganjian also recommends saving fun bath time accessories like bubble tab and colored water tablets for special occasions only.

"Kids don't need all that soap and fragrance on their bodies. We're seeing a sharp increase in sensitive skin and eczema in kids," he said, adding that chemicals can make those conditions worse. "Just plain warm water goes a long way."

For children with dry skin, adding a small amount of baking soda to plain bath water can help keep skin hydrated, Ganjian said.

By the time kids hit puberty, they might need to shower more frequently

Once your child starts entering puberty and needs deodorant, it's a good time to introduce daily showers. Ganjian recommends teaching children to wash their underarms and other smelly areas, which essentially sums up Kunis' approach to her daily hygiene.

"I don't wash my body with soap every day," she said on Shepard's podcast. "But I wash pits and tits and holes and soles."

While a daily bath might be a welcome part of your family's routine, there's no need to push it if you're finding daily baths stressful.

"I'm not saying you should have a smelly or oily kid," Ganjian said. "Your kid is going to be just as clean. But using soap and shampoo preventatively isn't needed."