Comparing four kinds of cooking oil at high temperature,researchers found that the Chinese rapeseed oil gave off 22 times more 1.3 butadiene, a potent cause of genetic disruption, than peanut oil did. The chemicals billowing off a hot wok included benzene, also found in cigarette smoke and known to cause leukemia, as well as what Shields called "chemicals of concern" : acrolein, formaldehyde and other aldehydes. "The smoke gets thick that some Chinese cooks keep the windows open even in winter," he said
The cooks use such roaring hot temperatures, he was told, to rid the oil of a lingering bad taste. Lowering the temperature to what an American cook might use to sauté vegetables, the researchers found the smoke content muchless hazardous. Adding the preservative BHA also reduced the amount of suspect chemicals. Shields continues to use a wok in his own home on occasion. He recommends using exhaust skillet or wok temperatures below the smoking point.