The humble potato chip requires a fairly simple recipe -- potatoes, oil and salt. The flavored potato chips? Less humble and at times, more complicated. Last month the FDA issued a warning letter to Frito-Lay, makers of Lays, Doritos, Fritos, Cheetos, Tostitos and Sun Chips after inspecting a manufacturing plant in California.

The FDA’s action followed several voluntary recalls from Frito-Lay.

A series of mistakes triggered the plant’s inspection. In the barbecue chips’ seasoning, a milk allergen was found. Original flavor chips and Cheddar and Sour Cream Ruffles were bagged together.

A plant inspection led to a recall because the chips “were prepared, packed or held under insanitary conditions whereby they may have been rendered injurious to health,” according to the FDA’s warning letter.

In a statement to Medical Daily Frito-Lay explained that “We are aware of the United States Food and Drug Administration (FDA) warning letter regarding recent Frito-Lay product recalls. Food quality, and ensuring strict adherence to food safety guidelines, are our highest priorities across all of our production facilities.” The company is working, the statement said, to fix any outstanding issues. “We look forward to resolving this matter quickly,” the letter said.

The FDA warning letter said that Frito-Lay had not adequately tried to stop mislabeling or contamination from one flavor to the next. Because some flavors contain allergens, like milk products, this could be especially dangerous.

It appears that no other Frito-Lay products were affected. Luckily, many chip flavors contain no milk products or whey and should be safe for everyone to eat. Frito-Lay has issued a recall on the Barbecue chips.