Kellogg Co. is voluntarily recalling about 28 million boxes of Apple Jacks, Corn Pops, Froot Loops and Honey Smacks cereals because an unusual smell and flavor from the packages' liners could make people ill, the company said Friday.

Kellogg said about 20 people complained about the cereals. The company said the potential for serious health problems is low.

Consumers reported the cereal smelled or tasted waxy or like metal or soap. Company spokeswoman J. Adaire Putnam said some described it as tasting stale.

Kellogg is trying to identify the substance on the liners that's causing the problem and is offering consumers refunds in the meantime.

The products were distributed throughout the U.S. and began arriving in stores in late March.

Only products with the letters "KN" following the use-by date are included in the recall. Products in Canada are not affected.

Kellogg's shares were almost unchanged Friday afternoon, trading at $52.69, 17 cents below Thursday's close.

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