The big lesson, and certainly the one I'd like to tell parents and doctors who see children, is that you should take whatever steps are necessary to prevent sunburn in children

Glenn Merlino molecular geneticist

The results showed that young mice went on to develop melanoma - the most serious form of skin cancer - in adulthood.

Thirty-fold difference

A single dose of UV radiation was enough to induce melanoma in the young mice.

In adults, 30 times more UV was needed to achieve the same effect.

Glenn Merlino, chief molecular geneticist at the institute, said that although the experiment had been confined to mice, the sun's dangerous rays could have the same impact on human skin.

He said: "The big lesson, and certainly the one I'd like to tell parents and doctors who see children, is that you should take whatever steps are necessary to prevent sunburn in children.

"They should wear hats, use sunscreen and avoid unnecessary exposure to sunlight."

In humans, melanocytes, the pigment-producing skin cells where melanoma develops, are on the surface of the skin; whereas in mice they are buried deep in the hair follicles.

In the Maryland experiment, which is reported in the science journal Nature, the mice were genetically modified so the melanocytes would appear close to the surface of the skin.

It is thought that some melanomas are the result of genetic damage caused when the UV radiation strikes these pigment cells.

Different skin

Babies and young children are thought to be more vulnerable because, in addition to mature melanocytes, their skin also contains more "melanocyte progenitor cells" - immature versions which precede fully-fledged pigment cells.

These progenitor cells divide and reproduce more rapidly when exposed to UV radiation.

It is feared that this rapid proliferation increases the chance that DNA damaged cells will reproduce and take hold, producing a tumour.

It is also thought that UV exposure could affect the developing immune system of the child, reducing the chances of an immune response which could destroy the developing cancer.

The genetically-engineered rodents, developed by Merlino, are the first to produce cancerous tumours that look and act like skin cancer in humans.

Melanoma accounts for roughly 10% of reported cases of skin cancer and can spread rapidly throughout the body, forming secondary tumours in the liver, lungs, bone or brain.