Zac Efron's kissing scene rules

Zac Efron has confessed he once embarrassed himself by eating tuna before shooting a kissing scene.

The High School Musical heartthrob admitted he was mortified by his mistake but insisted he has now learned to stay minty fresh before locking lips on-screen.

He told Access Hollywood: "No onions! I had a kissing scene one time and I ate a tuna sandwich and it was the first [scene] I had to do and I got called out on it.

"It was so embarrassing... You don't do that, don't be that guy!"

Zac gets up close and personal with Mercy actress Taylor Schilling in their new movie The Lucky One - the film adaptation of Nicholas Sparks' novel - and the star said he chewed gum before they had to smooch.

He also revealed he wasn't phased by their steamy scenes.

"You can't take it too seriously... I think the best way to do it is laugh all the way through it because it's hilarious," said Zac.