Scientists have devised a paint-on cream that, on mice, tans skin without the need for sunlight and also appears to offer some protection against cancer-causing ultra-violet rays, a study says.
Tanning is controlled by a body chemical known as melanocyte-stimulating hormone.
It works by binding to a specific area, or receptor, on skin cells.
But people with pale skin or red hair cannot tan efficiently because of a defect in this receptor, which means their skins tend to burn in the sun. Damage by ultraviolet light can eventually lead to skin cancer.
Researchers at the Dana-Farber Cancer Institute and Childrenâ€™s Hospital in Boston genetically engineered a batch of hairless fair-skinned mice that, tests showed, suffered burned skin when exposed to high doses of ultraviolet light.
The team smeared the rodents with a plant-derived compound, forskolin, that is known to stimulate the skin pigment melanin. The forskolin, derived from the root of an Indian plant called forskohli, turned the miceâ€™s skin dark.
In a second batch of experiments, a strain of cancer-prone mice that were also engineered to have deficient receptors, were exposed to daily doses of Florida-level noonday sun for between one and two hours for 20 weeks.
Nine mice which did not receive forskolin developed 11 skin tumors, while nine mice which received the forskolin developed six tumors and also showed fewer signs of skin damage.
In addition, the tumors among forskolin mice showed up three times later than the untreated mice. Put together, this amounts to significant skin protection, say the scientists.
â€œIt remains to be seen whether topical melanisation will be achievable in man, and whether it would afford measurable protection against UV skin damage and cancer,â€ they caution.
The study is published in the British weekly journal Nature.