Paint shop owners in Hanoi identified the dyeing chemical as the iron oxide yellow from China, according to ThanhNien News.com.

Many Vietnamese housewives prefer chicken with yellow skin believing that this means they are of Vietnamese origin and possess firm muscles.

“This is an industrial pigment used to dye wood before it is polished with veneer. Most carpenters buy the chemical to dye wood, but many (other) people are buying it for what purpose I cannot know,” said the owner of a paint shop on Hang Hom Street.

The owner, who didn’t want to be named, recalled that many people used to buy the brownish-black pigment at his shop to make fake chocolate ice-cream.

“That’s really dangerous, really terrible,” he said.

Nguyen Xuan An, a local resident, said paint sellers in the area understand the danger of industrial paints refuse to sell them to chicken hawkers.

“Chicken sellers lie when they buy the chemical,” Mr An said.

Iron oxide sells for VND90,000-150,000 per kilogram while Thai food coloring sells for VND330,000 a kilo on Hang Buom Street.

Dr Nguyen Xuan Mai, former head of Ho Chi Minh City Public Health Institute, said adding seasoning and color to foods can be okay. The question centers on what substance was being used in the coloring.

Dr Mai said the addition of industrial colors to food is banned as they are very poisonous and contain a lot of toxic metals.

Chickens fat quickly absorbs the chemicals which are then passed on to the consumer.

The doctor said iron oxide yellow can damage the liver and kidneys. It can also causes cancer, she said.

In early 2007, health officials in Hanoi kept discovering formaldehyde in pho noodles. The chemical was added to make the noodle tough and thus more tasty, they discovered.