Europe and now Asia face a growing scandal over the contamination of millions of eggs with the insecticide fipronil, which can be potentially harmful to humans.
Here is what we know about a scare that has triggered criminal probes and led to eggs pulled from supermarkets in 15 EU countries, Switzerland and Hong Kong.
What is fipronil?
Fipronil is widely used to rid household pets like dogs and cats of fleas and is effective at treating poultry for the parasite red lice.
But it is banned by the European Union for treating animals destined for human consumption, including chickens.
The World Health Organization says fipronil is "moderately hazardous" in large quantities, with dangerous effects on people's kidneys, liver and thyroid glands.
What is the risk?
Authorities in the affected countries say there is no risk to public health.
EU rules say eggs with a level of fipronil above 0.005 mg per kg must be withdrawn from sale even though there is no significant health risk.
Fipronil levels above 0.72 mg per kg are a possible "acute" health risk and should not be eaten.
When did it start?
The problem is believed to stem from a substance used by Dutch company Chickfriend, which farmers in the Netherlands and Belgium say they hired to treat their chickens.
A lawyer for a Belgian company, Poultry-Vision, says the firm sold it to Chickfriend but has not said where it got the substance.
Belgium has accused the Netherlands of having detected contaminated eggs as far back as November 2016 but keeping it quiet. The Netherlands says it was tipped off about the use of Fipronil in pens but did not know it was in eggs.
Belgium meanwhile has admitted that it knew about fipronil in eggs in early June but kept it secret because of a fraud investigation.
Belgium became the first country to officially notify the EU's food safety alert system on July 20, followed by the Netherlands and Germany.
The news did not go public until August 1.
What countries are affected?
Fifteen EU countries have received tainted eggs: Belgium, the Netherlands, Germany, France, Sweden, Britain, Austria, Ireland, Italy, Luxembourg, Poland, Romania, Slovakia, Slovenia and Denmark. Non-EU Switzerland and Hong Kong have too.
The eggs were imported from four countries—Belgium, the Netherlands, Germany and France. Farms in those countries where the banned substance was allegedly used to treat poultry have been shut down.
What is the official response?
The EU has called a meeting of ministers and food safety chiefs from affected EU countries on September 26 and called for an end to "blaming and shaming".
Investigators in the Netherlands and Belgium staged raids on Thursday, arresting two people at Chickfriend. Belgium says the head of Poultry-Vision was held for questioning in July, then released under strict conditions.
The EU says any countries found not to have notified Brussels immediately about the detection of fipronil could face legal action.
Explore further: What we know about Europe's tainted eggs scandal