Why do babies cry? Well, grand-mothers always know, of course. With a disapproving click of the tongue, they'll say: 'That baby's hungry. I can tell a hungry baby cry anywhere.' Or: 'That baby needs changing.' That the baby has just been fed and changed makes no difference, and only leads to more tongue-clicking and head-shaking. They know. Most of the time, there's a good reason for a baby screaming. It's their only way of telling us they need something. And, as far as babies are concerned, the louder the better - because their key to survival is keeping their parents on a tight leash. But every now and then some unfortunate parents find themselves dealing with a baby who seems to be inconsolable. This is a baby who screams no matter what you do, no matter how often you feed him, change him or burp him. And when a grandmother tells parents they don't know how to look after a baby properly (or words to that effect), it's hard to grit the teeth and keep smiling. So, there is, perhaps, strange comfort to be had from news that nobody really knows why a baby screams and is inconsolable. An American study just published in the Archives of Diseases of Childhood - which describes itself as 'providing the first systematic evidence of functional feeding problems in infants with colic' - has found that babies with colic usually have a feeding disorder. Colic is something every baby probably gets in the first few months of life. When they do, their parents are in for an exhausting time. It happens when the intestines go into spasm - usually because gas gets trapped in one of the coils, causing that excruciating stabbing pain we've all experienced just before a bout of food poisoning. The baby doesn't know what it is, but doesn't like it, so he draws his legs up and screams. But the type of colic the researchers in the US looked at doesn't go away. It's the sort that transforms a lovely gurgling baby into a crying monster who screams for hours and hours, day after day, week after week. The 43 babies they examined all cried for more than three hours a day, for three or more days a week, for at least three weeks. What did they find? Most of the babies studied weren't good at the rhythmic sucking and steady feeding needed to make food go into their guts in a smooth, easy way. They also didn't feed regularly - showing 'disorganised feeding behaviours' - and were often uncomfortable after a feed. Anyone who's fed a baby knows that most of them doze off gently as they feed. So, a baby who's irritable after a feed has probably let some of it go down the wrong way or sucked in a bit too much air. Knowing this may be of some comfort, but it doesn't cure the problem. What should you do if your baby is screaming you into a frazzled heap? The most important thing is to seek help early. This kind of problem can be psychologically and emotionally devastating for parents whose instincts drive them to respond powerfully to crying.