BEIJING, Sept 17, 2008 (AFP) - The industrial chemical melamine has been found in milk products produced by 22 Chinese dairy companies in an unfolding scandal that has killed three babies and sickened more than 6,000.

Following are key facts on melamine:

WHAT IT IS: An organic chemical rich in nitrogen.

MAIN USES: When turned into a resin and combined with formaldehyde it forms a plastic typically used in glues, plastic utensils and flame retardants. Its high nitrogen content also sees it used widely in fertilisers.

OTHER USES: Nitrogen levels are a key indicator of protein levels in a food product. Melamine is believed to be used widely in China to give the appearance of higher protein content in various animal feeds.

Foreign press reports have detailed a thriving Chinese market for melamine, which is made into a powder and then typically added to low-grade, corn, wheat, soy or other protein sources to create animal feed with the appearance of high protein levels.

DANGERS: Melamine is banned in food in both China and the United States.

It is not considered highly toxic when ingested. However, it has been shown to cause bladder stones and other urinary problems in lab animals, especially when it forms crystals after contact with other widely occurring chemicals.

Most of the babies who have fallen ill in China consumed the tainted milk powder for between three and six months. The three babies died of kidney failure.

IN THE NEWS: In 2007, melamine-laced food additives produced in China and later used in pet foods were blamed by US officials for the deaths of dogs and cats across the United States. A recall of several pet-food brands resulted.

In September 2008, melamine was found in the products of 22 Chinese companies that produce milk powder and baby formula, sickening babies with kidney stones. Chinese state media reports have said the melamine was added somewhere in the dairy production process to boost protein readings.

Sources: US Food and Drug Administration and media reports