So, Nancy and Arthur Cameron have nits – their father let it slip during an event at No 10. In fact it would be more of a story if the junior Camerons didn't have nits – because let's face it, why would the Prime Minister's kids be immune in the face of what is, by any standards, a national epidemic?
Nits are all around us: they're in a head near you, even if they're not in yours. According to leading UK nit expert Ian Burgess, director of the Medical Entomology Centre (it researches not only nits, but also cockroaches, fleas and bed bugs), between eight and 15 per cent of the school population is affected at any one time. And it's not just kids who get them, as many parents (including, perhaps, Mr Cameron) discover to their horror – maybe the people who sit beside him at cabinet meetings should move just a fraction further away, so there's no chance of catching them.
But oops, there's my first mistake! The problem with nits is, almost everything you thought you knew about them turns out to be nonsense. "They can't jump from head to head," says another nit expert, Christine Brown, a former school nurse. "You can only catch them if your head – and your hair – is in direct contact with that of an infected person. And what's more, what we're talking about aren't 'nits' at all. That word is commonly used to mean the insects, but what it actually means is the empty shell cases after the eggs have hatched."
So, here's the real lowdown on "nits". They're actually an insect called a head louse (plural: head lice). Their correct name is pediculus humanus capitis; and if you've got them living on your scalp, what you've got is a condition correctly called pediculosis capitis.
What's also true is that the incidence of pediculosis capitis has risen dramatically over the past few generations. I'm 48, and I never had head lice as a child and didn't have a single friend who ever had them either. A generation on, not only have all four of my daughters had them from time to time over the years – like all their friends – but I have caught them too, and so have most of my friends.
Is it embarrassing? Well, yes and no. The truth is that head lice used to be stigmatised as something that happened to unkempt-looking kids from the wrong side of the tracks; now we've all got them, they're almost a badge of pride. So you're a parent who hasn't ever found the odd louse in your hair, are you? And why's that, then? Not spending enough time with the kids, perhaps? If Cameron really does find anything crawling along his nit comb, he should hand it straight over to his newly-appointed spinmeister, Craig Oliver. It would, after all, be the best piece of hard-and-fast evidence that he is, as he's always maintained, still there in the thick of ordinary family life.
The big question about head lice, though, is why have they become so common? The usual answer is that they've become resistant to the pesticides used in anti-lice shampoos – so the population has grown and grown, and been relatively unchecked. But, says Christine Brown, that's not the whole story. The other problem, she says, is that when routine scalp inspections were introduced as part of the 1944 Education Act (leading to the establishment of an army of "Nitty Nora" nurses whose job it was to examine thousands of schoolchildren on a regular basis), parents stopped taking responsibility for the problem.
"Before that, lice were a problem that parents had to deal with – the knowledge was there in families, and if they were discovered people knew how to get rid of them," she says. "But that knowledge has disappeared. In fact, she maintains, "Nitty Noras" were spectacularly ineffective in detecting head lice infestations. "They were a complete waste of time. They couldn't possibly hope to detect the lice in every child's hair – they missed most of them."
What's more, "Nitty Noras" used to line kids up and check their hair when it was dry – and the best way to detect lice, says Jane Smith who markets bug-busting "nit-combing" kits, is to comb through wet hair with a very fine-toothed comb. Combing through hair that has been shampooed and still has conditioner on it is also, she says, an effective way to get rid of the lice: because when they're in danger of getting wet, the insects shut down their spiracles, or breathing-holes, and are immobile – and that, says Jane, is when you can comb them out. "If the hair isn't wet enough, they simply run from one side of the scalp to the other," she explains. "They move quickly."
They breed quickly, too, which is why – when left unchecked – an insect or two can quickly turn into an infestation. "The female lays five or six fertile eggs a night, so the population grows fast," says Jane. When they first hatch the insects are tiny – no bigger than a full stop – but full-sized they're the size of a match head.
Parents like me, who've had a houseful of kids for years and have lost count of the number of times they've had to get out the nit comb, are usually sanguine about the problem: but not so those with younger children. "Mothers phone our helpline in tears when they find lice in their child's head for the first time," says Jane. "They're so shocked ... they go to the GP, and the GP has no idea what to do. They go to the pharmacy, and they get information that's often incorrect." Her advice is to wet-comb the hair of everyone in the family every fourth day for a two-week period after anyone is found to have a louse or lice in their hair. "It does work, but you have to keep at it," she says.
She agrees that hairdressers can be particularly unhelpful – "I've heard tales of children who've been midway through a haircut, and the hairdresser has spotted a louse and refused to go on.".
But the bottom line is: do nits – or head lice, or pediculus capitis, call them what you will – actually matter? Given that they're so ubiquitous, and they're not actually life-threatening, should we bother about them at all? "Well... no one would think it's a nice idea to have lice living on their head," says Christine Brown. "But the other problem is that all that itching can introduce bacterial infections. And if an infestation really takes hold, and you're being bitten a lot, it can make your child feel really under the weather." Lousy, in fact – that is, in fact, the origin of the word. Let's hope the problem at No 10 doesn't go that far.
Animal life at No 10
Top cat Humphrey, named after the top civil servant in Yes, Minister, was Chief Mouser to the Cabinet Office and remains the most well-known Downing Street cat, serving under Thatcher, Major and Blair. He was "retired" when Cherie Blair took a dislike to him. Now a new cat is planned. Photos have been circulated among No 10 staff of the contenders, and in line with coalition protocol, the Lib Dems are being consulted on the name.
Dog days When Geoffrey Howe was Chancellor and lived next door to Thatcher at No 11, he had a dog named Budget. When he moved to become Foreign Secretary he was said to have changed its name to Summit.
Ratcatcher! It was during live TV broadcasts outside the world famous black door last month that rodents were seen scurrying around. A ratcatcher with traps in a Waitrose bag was later seen in the street.
Kestrel takes flight In 2008, a young kestrel had to be released from the No 10 garden, amid fears that it would fall victim to crows, cats and torrential rain.
Pig in a pen Farmers protesting about the state of the industry marched on Downing Street in March 2008, but were prevented from taking Winnie the pig who was kept in a pen across the road.
Busy bees Sarah Brown's attempt to soften the image of her Gordon's premiership included a makeover of the No 10 garden. Work involved installing "two bamboo bee boxes and a bumble bee house to give bees somewhere safe, dry and warm to hibernate for the winter".