The "challenge" is an experiment I'm conducting on my radio show, using myself as a human guinea pig. A few weeks back I interviewed the British writer and former Tory MP Matthew Parris. Parris hasn't washed his hair with shampoo for 15 years. He believes the whole shampoo industry is an expensive hoax. If you stop using shampoo, your hair will become increasingly lank, lifeless and greasy for about six weeks, after which it will fight back and achieve its own natural balance. Or so he claims.

JOCASTA FEELS A bit miffed on my behalf. I've written a fair few books and I've occasionally conducted a half-decent interview on the radio. But all anyone wants to talk to me about is my hair.

Last weekend we were at the Blue Mountains Music Festival, getting into some very bluesy guitar from Jeff Lang and people kept sidling up to me. "Your hair looks fine," they'd say, before adding, "You know, I'm on the challenge, too."

The "challenge" is an experiment I'm conducting on my radio show, using myself as a human guinea pig. A few weeks back I interviewed the British writer and former Tory MP Matthew Parris. Parris hasn't washed his hair with shampoo for 15 years. He believes the whole shampoo industry is an expensive hoax. If you stop using shampoo, your hair will become increasingly lank, lifeless and greasy for about six weeks, after which it will fight back and achieve its own natural balance. Or so he claims.

Parris says your hair will then become sweet-smelling, fluffy and clean and you'll never have to use shampoo again.

It was hard to resist the desire to test the theory and so I threw away my shampoo bottles, washing my hair vigorously, as he suggested, with nothing more than warm water. I am now entering week five of No Shampoo. Remarkably, many, many listeners have decided to join in.

The web page on which participants are recording their experience is receiving more hits than any such page we've ever set up. Emails flood in. People stop me on the street to explain their progress.

This, I think, is where the story becomes interesting. Why are so many people signing up for an experiment that, in its early stages at least, tends to cause men to crinkle their nose in disgust and women to run screaming from the room?

Here's my theory: in the 19th century workers complained of feeling like cogs in the machinery of production; a century or so on, there's something about modern consumerism that makes us feel like cogs in the machinery of consumption.

The corporations have us surrounded; they've measured us, tested us and sorted us into market segments. All they need is for us to stand still at our designated troughs and keep consuming. We feel a little tired of doing what we're told.

In this context, small moments of rebellion can be extremely pleasurable.

Could it be there's a whole aisle of the supermarket we could simply ignore - all those shampoos to leach the natural oils from our hair and all those conditioners to put them back again? And think, too, of the environmental gains: no more plastic bottles; no more chemicals on your skull and thence down the drain.

Of course, the No Shampoo challenge could leave us all looking like inadvertent Rastafarians - our hair matted into lank dreadlocks. My point is not to prejudge the outcome; more to note the pleasure we feel in breaking ranks, in questioning a consumerist orthodoxy.

This may be one of the real gifts of the current environmental crisis. In all sorts of ways, we're being encouraged out of our passivity, inspired to more engaged patterns of behaviour.

Consider, for example, the whole bucket-in-the-shower movement - the size of which dwarfs our nascent No Shampoo rebellion. This is where people place a bucket under the shower while waiting for the water to warm up. I must confess to have taken it up only in the past month or two. Strange fact: it's oddly pleasurable.

You fling the bucket in, push it to one side as you shower and then pad outside in your towel to pour it into a pot plant. I make no claim about its environmental impact: the quantities involved are negligible. And yet there's so much satisfaction in it.

Suddenly, you are looking at water in a fresh way. There's pleasure in the saving of it, in the walk outside, in the gift delivered to the plant. Hopefully, also in the taste of the parsley in a week or two.

It's only one of the chores that has come with the environmental crisis. And it strikes me how much I'm enjoying all of them. I enjoy the bucket in the shower and the walk outside to the compost heap. With the No Shampoo challenge, I'm enjoying saying "no" to a whole aisle of the supermarket - even if it means Jocasta is saying an equally fervent "no" to the idea of running her fingers through my hair.

I like, too, the way Sydneysiders now talk so obsessively about the weather; the way we stand watching the sky, hoping for rain, like a bunch of old bushies.

All these things - from the eschewing of shampoo to the talk about the weather - seem like a taking back of power, a series of small rebellions against passivity. Life seems better with these constraints than it did without them.

I scratch my head and wonder where this will all lead. I find I enjoy the scratching very much.

Must be the nits.