When Hollywood scenes get steamy, some celebs need to reach for mints before their on-screen lip-locks.

In fact, claims Los Angeles dentist Harold Katz, so many celebs have stinky breath that he's built a business of treating performers with halitosis.

"There are a handful of A-list movie stars, a lot of B-list. A lot of them are singers," said Katz, who describes himself as the "fresh-breath guru to the stars."

Katz won't reveal the names of any clients. But he did say one of the first celebs to visit him was a well-known singer who often appears in Las Vegas.

"One reason they're so concerned is that when they're singing they have their mouths wide open and people close to them," said Katz. "They're afraid of someone detecting bad breath on them." A white tongue signals a problem, so singers sometimes worry people will notice it.

Stars like Hugh Grant and Ben Affleck might not be such a huge draw at the box office if the audiences could take a whiff, according to some reports. And Clark Gable might not have made women yearn to kiss him the way Vivian Leigh did in Gone With the Wind.

"No one ever talks about stars with bad breath," said E! online columnist Anderson Jones. "Fame gives off such a powerful aura that it blinds us to the things that make these stars human."

Rumor has it cohorts of Grant begged him to eat a Listerine strip at last year's Academy Awards, according to Katz — who tried unsuccessfully to contact the Two Weeks Notice star about treatment.

"I couldn't get to him — he had an army of people around him," Katz said.

Affleck's leading ladies have also fussed about his icky breath, according to British newspapers, including the London Sunday Times and the Daily Telegraph.

"Sandra Bullock recently complained that her co-star Ben Affleck had smelly breath," the Telegraph wrote, after the duo worked on Forces of Nature.

And actor/director John Waters is yet another stinky star, according to Jones.

"He has some of the worst breath in town —  it's eye-watering," Jones said. "I suspect it's because he smokes."

Katz said poor diets or eating disorders are often among the culprits — as are more common bad habits. "Unfortunately people in show business drink a lot, smoke a lot," Katz said. "Alcohol-drinking is going to keep that bad-breath level high all day."

Boozing may have been at the root of Gable's problem — which was so acute Leigh reportedly hated doing kissing scenes with him.

Katz  measures clients' breath with a "halimeter." For those with high readings, he suggests sticking to a balanced diet, brushing the tongue and entire mouth in addition to the teeth, flossing, drinking water, sucking on his saliva-inducing mints and chewing sugarless gum.

To avoid awkward situations, many actors come to Katz before taping romantic scenes. "One of them (a soap opera actor) keeps coming back before kissing a new starlet," he said.

Another Broadway actor went to Katz because the woman he had to kiss in a play complained about his horrendous breath. Katz sent him an oxygenating mouth rinse from his "Thera Breath" line, which the actor would swig in the wings between scenes.

Not surprisingly, Katz said the rich and famous go to great lengths to keep their dealings with him secret.

The Vegas singer, for example, would have her driver scan Katz's waiting room to make sure it was empty. Other celebs make appointments under assumed names or have products sent to their assistants.

"A lot of them are very self-conscious," he said. "Their persona is that they're perfect."