Damage to skin cells might continue after exposure to UV

In collaboration with the Press Association

Damage caused by ultraviolet (UV) radiation could continue hours after exposure, according to a new laboratory study by US researchers.

"The best way to cut your risk of skin cancer is to enjoy the sun safely and avoid sunbeds." - Dr Aine McCarthy, Cancer Research UK

Exposure to UV light from the sun or tanning beds causes damage to the DNA inside cells called melanocytes, which make the melanin that gives skin its colour. This damage is one of the main causes of melanoma skin cancer.

It was previously believed that melanin protected the skin from harmful UV light, but this new evidence shows that this may not be the whole story.

“If you look inside adult skin, melanin does […]act as a shield. But it is doing both good and bad things,” said Professor Douglas Brash, lead author from Yale University.

The researchers found that melanin might play a carcinogenic role, as well as having protective effects.

When laboratory grown cells, both mouse and human, were exposed to radiation from a UV lamp, the radiation caused a type of DNA damage known as a cyclobutane dimer (CPD), which pushes the DNA out of shape and prevents it from being read correctly, leading to mutations that can cause cancer. 

The study, published in the journal Science, showed that the melanocytes generated CPDs immediately after exposure to UV light as well as continuing to do so up to three hours after UV exposure ended.

The culprit was found to be process called ‘chemiexcitation’ that stores energy from the sun, and releases it later.

Chemiexcitation has only previously been seen in primitive organisms.

Dr Aine McCarthy, science information officer at Cancer Research UK, said: "This important research increases our understanding of how UV radiation from the sun and sunbeds causes DNA damage that can lead to skin cancer.

"The discovery that UV radiation can continue to harm our DNA hours after exposure raises the possibility of developing future products that might reduce this 'dark damage'.

"But this doesn't mean that using after sun creams or other moisturisers will do anything to protect you against DNA damage. For now, the best way to cut your risk of skin cancer is to enjoy the sun safely and avoid sunbeds, " added Dr McCarthy. 


  • Premi S. et al. Chemiexcitation of melanin derivatives induces DNA photoproducts long after UV exposure, Science, 347 (6224) DOI:10.1126/science.1256022