In general, plastics that are marked with recycle codes 1, 2, 4 and 5 are unlikely to contain either BPA or phthalates. Time for a new bowl? The bottom line: when it comes to heat, there are no materials – short of ceramics – that don't leach something. We are assured however that whatever leaches into your food is "much lower than any threshold of damage". Hmmmm??? If, however, you still want to be extra cautious, you could choose to retire old plastic bowls, says Chris Winder, professor in toxicology and occupational health at the Australian Catholic University.

Plastics are large structures (polymers) synthesized from smaller building blocks called monomers. Even in plastic polymers that are "NOT" hazardous, the monomer may still be toxic on their own. In the right conditions, old plastics are more likely to break down into their monomers, he says. "If you have a melamine dish that's new and the monomers are very strongly bound to the polymer, then the release of the monomers is probably not that great. [Well that's reassuring!] "But if it's starting to get a bit old and in contact with things that would cause it to release these monomers, possibly including hot water... then I think that the risk is slightly higher."