Some, as they say, like it hot. And many are perfectly sanguine even when it is sprayed straight into their faces and eyes by a policeman. Officers in Cambridge, Massachusetts, are being counselled that pepper spray, a mixture of cayenne pepper and oils known as OC and used to disable people resisting arrest, is less effective against those who have eaten spicy food from an early age. "The people it doesn't affect are people who have consumed cayenne pepper from the time they are small children, and this generally breaks into ethnic categories," said Frank Gutoski, an instructor at Cambridge police academy. He says the spray is also ineffective against those who work with its ingredients in the fields or processing plants.

"Mexican-Americans tend to be pickers, so with Cajuns, Mexican-Americans, Pakistani, Indian, what happens is that OC is effective for a much shorter time." Frank Pasquarello, a police spokesman, said: "He's not slandering anyone, he's not making fun of anyone. He's teaching the class based on information he's received. "We've never been given any classes that say people from certain ethnic groups should be sprayed longer than others. You don't give a longer dose to someone who is Mexican, Latin American or Chinese." The innovative training technique did not meet with universal approval. "It seems crazy," said Jack Baugher, president of Security Plus, a pepper spray manufacturer based in Yakima, Washington. "It's like saying that because you're an iron worker you're less susceptible to being killed by a bullet."

Manuel Macias, a lawyer for central American refugees in Cambridge, said: "It's so ridiculous. But it's a laugh with an edge because of the knowl edge that these officers think you are physically different."

Others wondered how police could identify those who had ingested chilli or jambalaya. "How do you tell the difference if someone is a food-handler or not? By whether they have a chef's hat on?" said James Fox, a criminal justice professor at Northeastern university, Boston. "There are many Hispanics who can't tolerate spicy food."

Pepper spray causes severe burning for up to an hour after being squirted in the face and eyes. Mr Gutoski said he knew of the link between culinary habits and the war on crime from the Massachusetts Criminal Justice Training Council. But Kevin Harrington, the council's director, said: "This is something that's not condoned by our agency at all." Yesterday the Cambridge police commissioner, Ronnie Watson, said: "There is no empirical or scientific evidence to support these statements."