It's not usually clear why a tummy button (or umbilicus to give it its formal name) develops the shape and stance it does, and usually it has no implications for health whatsoever.

But there are some reasons why a protuding tummy button may develop, and in these cases treatment may be necessary.

Formation of the umbilicus in the unborn baby

The tummy button is formed by the point at which the umbilical cord leaves the unborn child. There's a gap in the strong muscles of the abdominal wall to allow the cord through. In the very early weeks of pregnancy, where there's rapid development of the unborn baby, this gap is very large and allows the intestines to develop mostly outside the body. Before the end of the first trimester or third of pregnancy, the intestines have moved back inside the abdomen and the abdominal muscles are growing together to close the gap.

Umbilical hernia

Sometimes, something like a small loop of intestines gets in the way to prevent full closure of the gap. This leaves a defect in the wall, which allows fluid, little bits of body tissue, and even intestines to protrude, resulting in the most common cause of a larger than normal tummy button - an umbilical hernia. The other main, but much rarer, cause is an infection of the umbilicus causing a large lump of scar tissue.

Umbilical hernias often settle without treatment

As many as one in three children may be born with a small umbilical hernia, but as the baby continues to develop the muscles close further and the hernia gets smaller and smaller until it settles into a normal sort of tummy button. This process continues for at least the first two years, by which time most umbilical hernias have resolved.

You can easily push gently on your son's umbilical hernia to feel the edges of the gap. If the diameter is less than 2cm (about 1in) then it's very likely the hernia will have closed on its own by the time your baby is four years old. Nothing has been shown to speed up this process, but until it closes the hernia is unlikely to cause any problems. Some hernias don't close themselves until a child is ten.

This article was last medically reviewed by Dr Trisha Macnair in November 2007