Although I've been coping with the incessant stranglehold of smog on Beijing with considerable calm, recent reports of tainted milk from New Zealand have sent a chill down my spine, because if proved true, it might have also harmed my 4-year-old son.

As I write this article, Chinese consumers are still waiting for an official risk assessment report after traces of a potentially toxic chemical were found in milk produced by Fonterra Cooperative Group Ltd, the world's largest exporter of dairy products.

Like many sensitive parents, I'd not be easily placated by assurances that "very low levels" of dicyandiamide, or DCD, in food don't pose a risk after going through the shockwaves of the 2008 tainted milk scandal that killed six infants and left more than 300,000 children with various ailments in the mainland.

Fonterra owned a large stake in the now defunct Sanlu Group, which was at the center of the crisis.

I'd once considered my son to be lucky. Born amid a national crackdown on melamine-contaminated milk when many scared urban parents vowed to keep their children away from domestic brands, he has always been fed milk formula from reputable foreign companies.

Until my son turned 2 years old, I had flown every three months to Shenzhen to buy milk in adjacent Hong Kong. Since Chinese mainland customs allows you to bring in a maximum of six tins at a time, I had to make more than one trip across the border between the two cities during each visit.

I knew people like me hauling baby formula in bulging trolley bags attracted resentful stares on streets and in the subway, because such runs on sales of milk sometimes caused shortages in the local market.

Our demand for foreign brands has also spawned an army of dedicated "parallel traders", who make a living buying baby formula in Hong Kong and selling them on the mainland at higher prices.

But what can we do? No parents will allow their child to eat food they are not reasonably confident about.