Tough lessons: Head lice don't necessarily prefer clean hair and humans aren't too far removed from our primate cousins.

Tough lessons: Head lice don't necessarily prefer clean hair and humans aren't too far removed from our primate cousins.

Adult life is full of petty humiliations.

Sometimes, they are due to unforced human error; energetic dancing among the over-40s, for instance, or the awful, ground-swallowing mutual horror created when a well-meaning person congratulates a non-pregnant person on her impending happy event. The bottomless-pit moment at which one realises a) that the gift one has just given an acquaintance for Christmas is actually the thing the very same acquaintance gave to one just 12 months earlier, and b) that the recipient has not been in the least bit deceived by the artful rewrapping.

Sometimes, humiliations are inflicted by the vicious world of inanimate objects. Drinking fountains that are stronger than you think and squirt you in the face. Poorlymade pants that split right up the back when you are on the bus on your way to work. Those horrible little plastic UHT milk-thimbles that detonate all over you. Lamp posts that cunningly place themselves in your path just exactly when you happen simultaneously to be walking at pace and sending a particularly amusing text message.

But there is one existentially scorching brand of humiliation that towers above all, and it owes its existence to the animal kingdom.

I speak, with grim and recentlyacquired expertise, of the Adult Nit Infestation.

Getting nits as an adult is quite different from getting nits as a child.

When you are a child, you genuinely don’t care.

And to the extent that you do, in any event, you will in all likelihood be absolutely satisfied with the assurance that “head lice prefer clean hair”.

(When I was a kid, I completely accepted this claim, filing it unquestioningly among other fascinating oddities from the natural world, like migrating eels, or the thing where in seahorse families it’s the dad who gets pregnant. As an adult, however, I recognise the clean-hair theory as a transparent piece of politically-correct propaganda. Why would a louse care whether hair is dirty or clean? And what choice does it have, anyway?)

As an adult, the discovery that one is harbouring an unspecified number of small scuttling insects in one’s hair brings about a number of confronting results.

The first is the immediate collapse of about 200,000 years of evolutionary history. Sure, you might be able to calculate Pi to 300 places, hold your end up in a conversation about neoclassicism, or construct a croquembouche. But once you’ve got things living in your hair, you’re starkly reminded that 99 per cent of your genetic code is pretty much straight-out bonobo monkey.

And for all the allure of the Paleolithic era, currently manifested in protein-heavy Paleo cafes and dinner guests who arrive with the declaration that they only eat dandelion leaves, crabapples and antelope, I’m guessing it probably stops – for most modern humans – well short of being a host animal for crawling things.

The second thing is the guilt.

Finding out that one is hosting nits gives rise to a delicate series of ethical questions.

Is there a disclosure obligation, as with awkward sexually transmitted diseases?

As I – cheeks aflame – explained to an Australian Broadcasting Corporation makeup artist this week that my hair was still on probation after several treatments of Agent Orange (forget the hippie eucalyptus stuff. I want those nits DEAD. I want their families DEAD), I felt somehow negligent as a human being. That I had failed my species.

In February, there were reports in California of a head-lice outbreak among teenagers, supposedly fuelled by the continuing popularity of selfies, in which people who barely know each other put their heads together for the purposes of securing a photo they can then show to other people they don’t know.

This was complicated news. On one hand, the idea of a Biblical plague of insects sent to punish obsessive selfie-hounds is deeply pleasing; it takes a very crafty deity indeed to decree that an excess of vanity be penalised with such a specialised disfigurement.

On the other hand, the public health ramifications of an Ebola-style spread of follicular contagion could be catastrophic.

One small family of lice, for instance, peacefully occupying the scalp of former prime minister Kevin Rudd in August and September 2013, could have unleashed a nation-changing epidemic.

At any rate, the excitable claims of a selfie-fuelled teen lice outbreak turned out to be largely spurious, based on the evidence of a “louse expert” in whose business - a nit removal salon called Nitless Noggins – a commercial interest in generating a nit stampede is clearly discernible.

Personally, I have decided to proceed without shame. I marched into my local pharmacy, and asked for nit poison with a clear voice and unlowered gaze. None of this “it’s for a friend” nonsense. 'My name is Annabel Crabb, and I had nits this week. I’m clean now. Selfie?'

Twitter: @annabelcrabb