Millions of eggs have been pulled from supermarket shelves in more than a dozen European countries - including the UK - after it was discovered that some had been contaminated with the potentially harmful insecticide fipronil.
Fipronil is commonly used to get rid of fleas, lice and ticks but is banned by the European Union for use on animals destined for human consumption, such as chickens.
The insecticide got into the food chain in the Netherlands, which is one of Europe's biggest egg producers, but contaminated eggs have now been found as far away as Hong Kong. There is no evidence yet that it has harmed anyone.
What is fipronil and is it harmful to humans?
Fipronil is a popular pesticide, often used to de-flea household pets such as dogs and cats. It is also effective at treating red lice, which are commonly found in poultry.
The World Health Organization (WHO) says fipronil is "moderately toxic" to people if it is eaten in large quantities, and can have dangerous effects on the kidneys, liver and thyroid glands.
It can also cause "nausea, vomiting, abdominal pain, dizziness, and epileptic seizures," says the Dutch food standards agency NVWA, although its effects are reversible.
Should we stop eating eggs?
NVWA has published a list of certain batch codes of eggs that should not be consumed. It said one batch in particular - with the code 2-NL-4015502 - could pose "an acute danger to public health".
While tests have found levels higher than the recommended EU limit of 0.72 mg/kg in eggs, both food standards' agencies and toxicologists are playing down the risks for anyone who has already eaten contaminated eggs or other food products they were used in.
Dutch toxicologist Martin van den Berg told local media that it would only be harmful "if you eat them every day throughout your life."
The German food standards' agency said that an excess of fipronil in the short term "does not automatically mean that consumption of the food in question involves a health risk".
The UK's Food Standards Agency (FSA) said 700,000 eggs imported to Britain had been affected, up from an earlier estimate of 21,000.
But it cautioned that this number represents only about 0.007% of eggs consumed in the UK each year and that it was "very unlikely there is any risk to public health from consuming these foods".
Where and how did the contamination originate?
The contamination was discovered on Dutch poultry farms, and some 180 farms - which produce millions of eggs a week - have been temporarily shut down while further tests are carried out.
It is thought that Fipronil was used in chicken farms to combat lice, affecting the eggs of laying hens.
A criminal investigation is now under way in Belgium and the Netherlands, centring on two firms - Poultry Vision, a pest control firm from Belgium, which is alleged to have sold the treatment to a Dutch poultry farm cleaning company, Chickfriend.
Those firms have not yet publicly commented on the allegations although the AFP news agency reports that a lawyer for Poultry Vision has confirmed the firm sold the treatment to Chickfriend, but did not say where it had come from.
A number of police raids have been carried out in the two countries in connection with the contamination, and Dutch police have arrested two people.
What has been the political reaction?
The scandal only became public in late July, and soon after eggs were pulled from supermarket shelves in the Netherlands, Germany and elsewhere. It has since continued to widen.
Belgium came in for criticism when it emerged it knew about the fipronil contamination in early June but did not notify the European Commission until late July because of a fraud investigation.
However, Belgian Agriculture Minister Denis Ducarme has since hit back, accusing the Dutch of knowing about the problem as far back as November 2016. The NVWA has rejected the claim.
The European Commission's food safety chief has called for an end to the "blaming and shaming". The commission will hold a meeting with ministers and regulators on 26 September.
But the suggestion that fipronil may have been in the food chain for longer than previously thought has alarmed many.
German Agriculture Minister Christian Schmidt called the circumstances "criminal".