Here's good news for cooks: Japanese scientists say they might have found a way to produce onions that won't make you cry.

Ordinary onions, when chopped or crushed, create and release an eye irritant that makes tears flow in the kitchen. While some onions are called "tearless," they're actually just less prone than other varieties to cause eye irritation.

Scientists thought they knew the chemical steps that occur in the onion to produce the irritant. But in the Oct. 17 issue of the journal Nature, Japanese researchers report discovering a previously unknown enzyme that plays a key role. If they can block that enzyme, they suggest, the result might be an onion that doesn't produce the irritant. So, no tears.

The work is reported by Shinsuke Imai and colleagues at the House Foods Corp. in Chiba, Japan. In an e-mail message, the researchers said they believe they can suppress the enzyme without significantly altering the onion's flavor, and that their next step is to see if that's true.

In fact, stopping the tears might mean altering the flavor in unpredictable ways, said Eric Block, an expert in the chemistry of onions at the State University of New York at Albany.

It could change the proportions of substances in the onion that affect flavor, he said. And the eye irritant itself contributes to the flavor, such as by producing a slight burning sensation on the tongue, he said.

"Some of us kind of enjoy that experience," Block said. "You can mess with the onion, you can change it, you can maybe make it tear-free. Is that a better onion? Some people might say it's inferior to the palate."

His own work also suggests that the altered onion might promote heartburn, he said. The Japanese researchers said they doubt that.

Block said the chemistry is too complex to make firm predictions about what an altered onion would be like, and that the only way to know is to make one, as the Japanese researchers plan to do.

As for current onions, cooks can avoid the eye problem by chopping them under running water or an exhaust fan. "It's something we can easily live with," Block said.