Some 28 people were arrested after the raids Wednesday in two towns in Uttar Pradesh state, police official Brij Lal said. Some 264 gallons (1,000 liters) of synthetic milk were seized.

"Milk products manufactured from urea, caustic soda and animal fat were recovered from two makeshift factories," Lal said.

Diwali, the Hindu festival of lights, is on Saturday and it pushes up demand for milk and milk products that are used to make traditional sweets that are consumed and gifted during the holiday.

"During the festive season the demand of sweets goes up and people manufacture synthetic milk to meet this demand," Lal said.

The synthetic milk is prepared by mixing urea, caustic soda, cheap cooking oil and common detergent. Detergents are added to emulsify and dissolve the oil in water giving the frothy solution the color of white milk, according to N.C. Khanna, a scientist at the Indian Institute of Toxicology Research.

Refined oil is used as a substitute for milk fat and the synthetic milk is added to natural milk before it's sold, he said adding that caustic soda is added to the blended milk to neutralize the acidity, thereby preventing it from turning sour.

Doctors say that the synthetic milk is carcinogenic and the urea and caustic soda are very harmful to the heart, liver and kidneys.

"Caustic soda could prove fatal for people suffering from hypertension and heart ailments," Dr. Lalit Saxena said.

"Please do not eat sweets this Diwali. Avoid them as there is no guarantee of its purity," said Dr. D.P. Mishra of the state-run Balrampur Hospital in Lucknow.