A 67-year-old woman vomited and felt numbness on her tongue after eating Nissin's Cup Noodle this week in the Tokyo suburb of Fujisawa, the city's health office said late Thursday.
The product was made at a Nissin factory in Japan. A series of previous scares have involved food imported from China.
The health office said on inspecting the Cup Noodle they had discovered paradichlorobenzene, the key chemical in bug repellent, but no puncture or other abnormality in the cup.
Nissin was voluntarily recalling around 500,000 cups made on the same factory line the same day, a company spokesman said.
They were sold at supermarkets in Tokyo and neighbouring areas with most of them already gone from store shelves, he said.
"We apologise for causing trouble to Cup Noodle lovers," Nissin president Susumu Nakagawa told reporters late Thursday.
However, he denied the possibility of contamination at the factory, saying it had never used or stored the insecticide and had seven security cameras watching manufacturing lines.
"It is unthinkable that the contamination occurred at our production lines," he said.
The noodles scare spread Friday as another company, Myojo Foods Co. of Tokyo, said it found instant noodles laced with paradichlorobenzene and naphthol, also used as bug repellent.
A man "poured in hot water and noticed chemical smells," said a health official in Yososuka, southwest of Tokyo. The man was unhurt as he did not eat the noodles.
Nissin, based in the western Japan city of Osaka, created instant ramen noodles as Japan's economy grew rapidly after World War II. Aimed at busy people on the go, it has since become a multibillion-dollar industry.
Japan has been on alert after a series of health scares involving food, mostly made in China.
Earlier this month one woman fell sick after eating frozen green beans imported from China, which were found to contain thousands of times the permissible level of pesticide residue.