As a mother of an autistic child, I've heard autism put down to everything from eating tuna fish to watching too much telly.
On several occasions I've been cornered by a peddler of the latest theory who claims to have The Truth.
These 'truth-tellers' always have scary bug eyes, which never blink.
They come bearing glad tidings: your child is actually completely normal. He has been bewitched by some aspect of The System, such as Capitalism or The Doctors or The Government. A few drops of whatever they're selling and your child will be fine again.
This Truth is always just the latest conspiracy theory. The most enduring of these in relation to autism has been the one which blames the MMR measles vaccine. It has endured because it exploits our fears of being controlled by The System.
It makes unlucky parents victims and gives them someone to blame.
And it reassures would-be parents that if they avoid the MMR their children won't be autistic.
It is complete bull. The doctor who dreamed it up has been struck off. His theory is a simple case of fraud.
But it has caused thousands and thousands of parents not to vaccinate their children against measles.
Now there's an upsurge in cases of measles all over Europe. Six deaths have been recorded in France this year.
In Ireland there have been 135 confirmed cases, most of them on Dublin's northside.
Half of these kids have not been fully vaccinated.
We can't blame poverty for this. We can't blame the Government. Vaccination is freely available in every doctor's surgery. There's talk of special clinics being set up in schools in north Dublin.
The Somali mother I heard about by chance on RTE radio during the summer was not so lucky.
She walked miles and miles to the city of Mogadishu looking for food with her three starving children. When she got there she made them a house out of cardboard boxes and cement bags.
But she couldn't protect them.
Two of them died of measles in one night. The third, who survived, was the only one vaccinated.
She keened, and rocked and blamed herself. But it wasn't her fault. She had missed the vaccine through poverty, not choice.
But we let a conspiracy theory get between us and choosing to vaccinate our kids.
You can avoid measles if enough people get their kids vaccinated.
But you can't avoid autism. It's mostly genetic but there are probably other factors which make it more likely.
They probably come into play very early in a pregnancy. And we don't know what they are.
Science is working away at finding out. Meanwhile, science has already found out how to avoid measles and many of us don't want to know.
We don't know anyone like that Somali woman. We don't know anyone whose child has died of measles. Many of us know no-one whose child has died. Children dying of preventable diseases is the kind of thing which has been consigned to history.
By vaccination. That's what we forget.
But autism is not going anywhere.
Many of us have autistic children, many of us know others who have them. Just tonight a mum whose child has just been diagnosed rang me and asked: "What do I do now?"
And because we just can't accept that bad things happen we have to find someone or something to blame. But there's such a thing as bad luck. There's such a thing as accepting fate. Because, ultimately, that is accepting your child.
This hysterical search for someone or something to blame for autism makes acceptance so much harder.
And the blame game is everywhere. The parents who have lobbied for the intensive behaviour training called Applied Behaviour Analysis (ABA) for their kids have done great work. But I have heard the media portray ABA as a cure for autism. I have heard them more or less blame gaps in ABA provision for making children autistic.
There is no cure for autism. There is no vaccine for autism. But there is a vaccine for measles.
You might say you'd rather chance the measles, but here's a thing: autism won't kill your child, but measles might.