Scientists in the UK have developed UV-sensitive "intelligent inks" that change colour when there is danger of sunburn and can be tuned to suit different skin types, which is something that current UV dosimeters can't cope with. However, they also said the challenge will not be cost or technology, since the indicators are cheap and easy to make, but getting sun lovers to use them.

Professor Andrew Mills and colleagues from the University of Strathclyde, Glasgow, carried out the research that led to the discovery and describe it in ChemComm, a journal of the Royal Society of Chemistry.

Mills and colleagues wrote that over exposure to UV radiation is known to be dangerous to health. Short term exposure can lead to sunburn (erythema) and conjunctivitis, while long term exposure can lead to photo-aging, cataracts and skin cancer, for which in the UK alone there are over 70,000 new diagnosed cases a year, of which 9,000 are malignant leading to around 2,000 deaths. They wrote that the problem is increasing as suntans become increasingly perceived as a sign of "health and wealth".

Unfortunately, sunburn symptoms take up to 48 hours to show, which is too late to take precautions. The problem with current makes of UV dosimeters is that they can't distinguish different types of skin, and their colour also changes gradually with sun exposure, making it difficult to judge the risk.

But Mills and colleagues say they have come up with a "simple, inexpensive, unambiguous" sunburn indicator that can be adapted for different types of skin. It could cost as little as 20p a strip (about 20 to 30 US cents) and could be worn on a bracelet or sticky label on clothes.

The indicator they developed relies on an acid-releasing chemical that is activated by UV light, and a pH indicator dye that changes colour as the acid increases in strength. Thus, as the indicator absorbs more UV rays, the more it changes colour.

By using different acid-releasing chemicals and dyes, different indicators could be developed for different skin types, said Mills.

Professor Peter Roberston, an expert in photocatalysis at Robert Gordon University, Aberdeen, told Chemical Technology magazine that he was gratified to "see academic science coming up with a solution that is going to have an impact on society".