Babies in crash helmets pass without comment at playgroups in the US: here, they still raise an eyebrow. "People look at Ben and they stare - you see them thinking, oh, that poor family," says Karen Saich. "You can tell what's going through their minds: the baby is so little and he's obviously been in a car accident or he's got epilepsy ... how terrible for them."

In fact, her eight-month-old son is entirely healthy save for one problem: a couple of months after he was born, Karen realised his head was a slightly odd shape. He had a flat patch to one side of his head, his ears were slightly out of alignment and one cheek appeared more prominent than the other. "I noticed it one day when I was looking down at Ben's head as Philip, my husband, was feeding him," says Karen. "It suddenly looked very obvious ... we weren't sure what it meant, but we thought we'd talk to the health visitor."

The Saiches' health visitor advised that, since a baby of Ben's age has fast-growing, soft bones, it could be that his head growth was uneven because he was tending to favour looking to one side of his body. She was not overly concerned, since she thought the problem would right itself over time, but she told the couple they could try to get him to look the other way. "Ben did spend almost all his time facing to his right," says Philip. "We did as the health visitor suggested and moved all the toys in his cot to his left side, but it didn't make much difference - he seemed to want to look only to his right."

The Saiches were mulling over what to do next when Karen found herself at a playgroup near her home in Gamlingay, Cambridgeshire, where there was a baby in a white, polystyrene crash helmet. "I started chatting to the mother and within minutes it was clear that this baby had exactly the same problem as Ben - and I now realised it had a name, plagiocephaly. By the time I left I had the details of the specialist and I was determined we'd find out all we could about our baby's condition."

The Saiches contacted the specialist, German maxillofacial and craniofacial surgeon Chris Blecher. One of only two medics in the UK to treat plagio, he was at that time running a fortnightly clinic in London. "We sent pictures of Ben by email," says Philip. "A couple of weeks later we had our first consultation. Chris took some measurements and found that Ben's skull was 21mm out of alignment - in his book, that counts as severe and he said that, if we wanted him to, he would treat Ben using a helmet."

The helmet, Blecher explained, would be an exact fit for Ben's head: but while it would fit snugly everywhere else, it would have an opening at exactly the points where his skull was flattened. In other words, head growth over the weeks ahead would be channelled towards the area that needed to "catch up".

A head cast was taken straight away, and a fortnight later Ben was back at the clinic for the helmet he has been wearing ever since for 23 hours out of 24. "It's a very emotional decision, working out whether it's the right thing to do," says Philip. "You desperately want the right thing for your child. But in fact Ben hasn't been at all perturbed by his helmet - and the good news is that, when we went back to see Chris again after six weeks of the treatment, the misalignment had reduced from 21mm to just 5mm - an extraordinarily good result, according to Chris, and probably due to Ben being exactly the right age for the treatment."

The Saichs are delighted their son's head will now be "normal" shaped - although some might baulk at the idea of spending around £1,500 correcting what seems like a minor cosmetic problem. Most NHS paediatricians are dubious about the need to use helmets - the conventional medical view is that it doesn't much matter if a baby's head is slightly misshapen, as hair will cover up the problem and there are no long-term medical implications.

Philip Saich doesn't agree."What we feared was that, by the time he reached school age, Ben's head might make him the subject of bullying," says Philip. "We were also worried that if he ever needed glasses it would be difficult to fit them because of his ears being misaligned. And once I'd looked on the internet and come across other stories, I was worried about possible jaw and dental problems, and even about whether an odd head shape could cause migraines in later life."

Orthotist Stephen Mottram, who works for the US company Medistox, is the other medic treating plagiocephaly in the UK. He says it's impossible to know how many babies have misshapen heads - some surveys have suggested as many as one in four, others as few as one in 300. What is clear, he believes, is that the condition is more common in boys than girls, and that it is on the increase - caused, at least partly, by the "back to sleep" campaign which has, in the last decade or so, reduced the number of cot deaths by persuading parents to lie their babies to sleep on their backs.

"No one would argue with the back to sleep campaign," says Mottram. ""Although putting your baby down to sleep on his or her back is important, so too is tummy time. Babies often don't like being laid down on their tummies to play, but they do get used to it - and as well as the advantages for their head shape, it also helps develop their neck and spinal muscles.

"Where a baby seems to be developing plagiocephaly, my first suggestion would be to move the baby so he isn't always sleeping with his head to the same side." But even with tummy time and repositioning, some infants continue to have an unusual head shape: other possible causes include a reduced amount of amniotic fluid during pregnancy, an instrumental delivery and a condition called torticollis, which means the muscles on one side of the baby's neck are shorter than the other.

Where the condition persists, the window of opportunity to correct the child's head shape is very limited: by the age of 14 months, says Mottram, the soft spots or fontanelles in a baby's head - which allow for the fast period of growth in the first year - are fused and the skull geometry is set. "So if you want to do anything to change the head shape, things really have to happen fast."

The Saiches and Mottram say they're disappointed that the NHS doesn't offer more to parents concerned about their babies' head shape. To give parents more information, offer advice and share success stories, Philip and Karen have launched a website, headstart4babies.co.uk. "Doctors in the UK say there isn't enough published evidence that the helmets work or that the treatment is necessary," says Mottram. "But our results suggest that the helmets can make a huge difference - provided they're available at the right time in the baby's life.

"In the US, babies with helmets are commonplace. In the future, I believe we'll see helmet-wearing in babies much as we see brace-wearing in older children - as a useful device to give a child the best start in life."