But now, it turns out, scientists from Nanyang Technological University have found that nanoparticles of zinc oxide, a substance used in many sunscreens and cosmetics, can cause a chain-reaction cascade that leads to cancer in lab-grown cells.

Cue alarm and frantic consumers saying: But I thought it was natural!

So is zinc oxide, that innocuous-looking white smear across a sunbather's nose, really a carcinogen?

The honest answer is: It depends.

Or as doctors might say: It's all about the dose.

The links between environmental toxins and the incidence of disease in real life, rather than in the lab, are some of the toughest in the world to prove. This is just because in real life,  scientists can't track everything that people wear, eat and smear on themselves. (The exception is when there is a very strong link between, say, pregnant women consuming thalidomide and the incidence of birth defects.)

But here are some useful questions to ask about products containing zinc oxide, or any other potentially harmful substance.

How much?

Does the product contain a high concentration or low concentration of the chemical? That has an impact on the level of the chemical users are exposed to.

What size are the particles?

The potential environmental effects of nanoparticles in general are known. Scientists know that at a high enough dosage, free-floating silver nanoparticles can cause birth defects or even kill zebrafish embryos, and that they might be able to enter the human body easily because they are so small.

What's the degree of exposure and what part of your body is exposed?

Are you wearing the stuff all day, every day? Injecting it into your body? Or swallowing it?
As for degree, some nail polishes contain solvents that evaporate into nasty fumes. I like to paint my nails, but I do it in a well-ventilated room once in a blue moon. (But I would worry about the health of manicurists in a poorly ventilated salon, for example.)

Closer to home, vitamin A, that eyesight-promoting vitamin good for your skin and teeth - is poisonous in very large quantities. But you would have to consume enough carrots to turn you bright orange in order to feel the effects of vitamin A poisoning. So I will probably keep saying yes to carrots.

One more thing, about the word 'natural': Just because something is natural does not mean it is non-toxic! Arsenic, for example, is a naturally occurring element that gets into well water in Cambodia and Bangladesh. No one goes around blithely drinking arsenic-laced well water just because it is natural.

Finally, there's one more important question: Which carries the higher risk - tiny nanoparticles of zinc oxide (or anything else, really) in your sunscreen, or skin cancer from going without?

That's one statistic I would like to find out. Again, the answer is probably,  'It depends...'

Some, like my colleague Ong Sor Fern (http://www.straitstimes.com/PrimeNews/Story/STIStory_691107.html), argue that they would be a waste of money.

I'm going to argue that they represent some of the best value for Singapore, that money can buy.

By definition, a natural history museum is a story about the world's life and evolution. So it must go beyond Singapore's own natural history, rich as that itself is.

It would be parochial and somewhat myopic to say, oh, these dinosaurs weren't even found in the region.

Would our art museums turn down the chance to show off a Da Vinci or a Rembrandt just because they weren't Singaporean painters?

I hardly think so - or at least, they would think long and hard before turning one of the Old Masters down.

So it is with dinosaur fossils - specifically the diplodocid sauropods, the long-necked, plodding favourites of children's movies like Land Before Time.

As my colleague Ignatius Low put it (http://www.straitstimes.com/Lifestyle/Reflect/Story/STIStory_691416.html), they would give Singapore a sense of its own place in geology and time - putting the ambitious little city-state in its place while at the same time, teaching its children to dream big.

"We live in a fast-paced global city of commerce where the next transaction, event, project or career move is often all that we have on the horizon. Few things in this world would give us a more instant perspective on life than standing there, all tiny, next to some of the biggest creatures that once roamed the earth but were suddenly extinguished by Nature," he wrote.

NOT JUST MONEY-SPINNING

You see, it's not about a blockbuster show. It's not about fossils being money-spinners. It's about children.

A museum gallery dedicated to the social and cultural history of fashion is appreciated by only a handful of adults.

But the natural history museum is for the Singaporean children - of all ages - who will tramp through it on school excursions, to surround the towering fossils and gape.

Do we or don't we want our children to grow up with that sense of wonder? Don't we want them to think beyond the local, to grow into citizens not only of Singapore, but of the earth?

That's why $12 million, not even of taxpayer money but charitable donations, is a bargain.

In Singapore education-spending terms, a $12 million price-tag is a drop in the bucket.

This year alone, the Ministry of Education budget for primary and secondary schools, special schools and junior colleges, is more than $5 billion. And dinosaurs are in themselves, an education.

Of course, it is necessary to also train curators and scholars, the experts who can explain the significance of these dinosaurs and put them - and Singapore - in their context in geologic and biological time.

But that will come when we see the value of having dino fossils in the first place.

It’s a cheap shot, but they’re usually right. After all, these are conferences about saving energy, reducing greenhouse-gas emissions and rescuing the earth.

The same sort of cheap shot was made at this weekend’s National Sustainability Conference, organised by the National University of Singapore.

Frankly, though, this conference was better than most.

Not a plastic bottle in sight, food waste was composted in the NUS kitchens and the conference programme was not only double-sided, but half-sized to save paper. The meeting even claimed to be the first carbon-neutral conference held in Singapore.

This was a step up from other conferences I’ve attended, where plastic bottles (ok, of Newater) were handed out like...water, programme notes were on fat single-sided sheets and every participant was given his or her very own styrofoam box of delicious, well-travelled (in food miles) lunch.

And each year, policymakers and climate-change negotiators are derided for holding their United Nations Framework Convention on Climate Change talks in places as far-flung as Bonn and Bali.

How many thousands of air miles do these administrators travel, detractors cry, and how much CO2 do they emit in the process? How much paper do they use? How many trees?

I’m going to propose a double-barrelled solution.

First, I think conference organisers should at least be conscious of the environmental costs and take the sort of steps that the National Sustainability Conference took to reduce waste and emissions.

And second, let’s look at a conference in a whole new light.

Never mind its environmental footprint (though this should be as small as possible), what is its final outcome?

How much real progress is made as a result of a conference, compared to its environmental impact?

With all the air miles and food miles and plastic waste and trees felled, the academics, administrators and policymakers (and the journalists) should have some real changes to show for it.

The bigger the environmental footprint, the bigger the policy change I’m going to expect.

That’s what I call bang for my buck.

If selected for the trip, I would ski more than 800 km to the South Pole, in well-below-zero temperatures, dragging a sledge that weighed the same as I do. Sort of like mushing sled dogs, only without the dogs.

"You don’t have any natural insulation! You’ll freeze," my friends squealed.

"It’s so dangerous," my father said.

Even I thought I was insane. The sum total of my athletic experience consisted of trudging up a couple of Malaysian mountains and falling over my cross-country skis while at university in New Hampshire. Forget marathons, I was content to run a few kilometres on Sunday mornings if I could get out of bed.

Then came the e-mail telling me I’d been shortlisted for an interview. Insanity turned into a spark of hope. The actual possibility of going to the South Pole sank in.

Yesterday, I didn’t make the final cut, and the spark of hope faded again. Sure, I was disappointed, but the experience drove the point home: I could and should dream big, test my physical and mental limits.

For two of my fellow applicants, Sophia and Lina, that dream is still alive. They’re ordinary women like the rest of us - attempting extraordinary things. I’ll be watching their journey and cheering them on every step of the way.

And as for me? I think I’ll sign up for that half-marathon now.

Read more about the Commonwealth Women’s Antarctic Expedition in today's edition of The Straits Times.