US scientists say that a common form of skin cancer, basal cell carcinoma, gives off a distinctive chemical "scent", which could be used for early skin cancer diagnoses.

Researchers from Philadelphia's Monell Center sampled the air directly above basal cell carcinomas and found it to be different to similar samples from healthy skin. This finding offers a chance of early, cheap and painless testing.

Other scientists have already done similar things such as spotting the "smell" of cancer by using dogs to sniff out bladder tumours from urine samples. It was UK researchers who had trained dogs to detect subtle changes in the odour of urine indicating bladder cancer, and possibly prostate and skin cancers real soon.

All human skin releases chemicals called "volatile organic compounds", many of which do have a scent. UK scientists believe that the dog's nose is one of the most sensitive instruments available that had the advantage of being attached to a brain already programmed to identify different patterns in the scents it received. They see this as a great potential as a screening tool that is so simple and non-invasive.

Researchers from the Monell Center used a technology called gas chromatography-mass spectrometry to identify their precise chemical composition. They included a total of 22 patients, 11 with and 11 without basal cell carcinomas for testing. All the air samples contained the same ingredients, but the equipment revealed that the patients with cancer had markedly different concentrations of certain chemicals.

The researchers now believe that they could build "profile" of the cancer to help them diagnose skin cancers at very early stages. They are now onto constructing profiles of other types of skin cancer, including the much more dangerous form - malignant melanoma.