Kristen Bell caught ''anal worms'' from her daughter.

The 37-year-old actress couldn't stop scratching her butt after she contracted pinworms - also known as threadworm - from her three-year-old daughter Delta.

Speaking on 'The Joel McHale Show', she said: ''It was very itchy. Fifty percent of people over 15 don't experience symptoms, which is the itch. Your kids get them because they put their hands in their mouth and they lay eggs.''

The 'Bad Moms' star first realised there was something wrong when she went to pick Delta and her other daughter Lincoln, four, up from pre-school and noticed the carpets were being ripped up because of the pinworm outbreak.

She explained: ''Of course I immediately Googled it, and it's like, so, so contagious. You have to monitor and you have to look in their poop. And when you wipe their butt, sure enough, I wiped and saw a little white worm. I know, she's really gross. My daughter, not the worm. The worm was gross, too.''

Although it's a highly contagious infection, Kristen's husband Dax Shepard and Lincoln managed to avoid catching the parasite thanks to a preventative cream.

And, despite catching worms from the school, Kristen admitted she and Dax chose to send the girls to that nursery because it encourages ''emotional learning.''

She said recently: ''When the kids get physical with each other - which they do because they're all feral at this point - they teach them to say things like: 'I don't like it when you touch my body like that.'

''They say that to me: 'I don't like having my hair touched.' ''

The blonde beauty recently revealed she has cut down on using the phrase 'it's OK' around her brood, because she thinks it ''shuts down'' their ability to express.

She explained: ''I do really like reevaluating how much we say to them, 'It's OK,' because it weirdly shuts down their ability to have emotions. Because they think, 'It's OK. I shouldn't be embarrassed. I shouldn't be sad.' So now when they get sad or embarrassed, I say, 'That's a stinky feeling, huh? I've felt it, too.' I just let them experience it, and hopefully it'll make healthy adults ... The one finger rule was something I really enjoyed. They said, 'Let your toddler experience things.' Like, 'I wanna touch that vase!' Rather than always saying, 'No,' you say, 'Let's do it! Let's do one finger.' So, my toddlers go around and touch everything with one finger.''