British scientists warned on Thursday exposure to filtered sunlight is still dangerous. They said sunlight at the break and end of the day still places people at the risk of acquiring skin cancer.

The basis of their warning is a study on differences between Ultraviolet B (UVB) and Ultraviolet A (UVA) radiation. The study was published in the Journal of Investigative Dermatology.

UVA1, which makes up 75 per cent of sunlight, was found to damage a deeper layer of the skin. UVA1 radiation can pass through windows and glass, but are less dangerous compared to UVB which act mainly on the outermost skin layers where cancers frequently occur.

The UVA2 radiation is the type used in tanning beds. Darrel Rigel, clinical professor of dermatology at New York University Medical Center, pointed out that people generally were more concerned with UVA 2, which is closer to UVB, than to UVA1.

However, the new study by London researchers showed that UVA1 could produce the same types of DNA damage similar to early skin cancer.

"What we are saying is that UVA does cause significant damage to DNA in the skin especially in the base layer, and that is where the damage is important.... Damage to the upper layers is not so important because those layers are in the process of dying, whereas damage to a dividing cell is more worrying," The Telegraph quoted Antony Young, one of the researchers from King's College London.

Mr Young explained that because of the UVA radiation focus on lower layers, the serious damage it causes often go unnoticed since the outer skin layer is not burned. He said people who are exposed often to the sun while inside vehicles are at a similar risk because the window or sunroof glass filters out UVB radiation, not UVA rays.

Mr Rigel said the findings underscore the importance of using sun protection such as hats, proper clothing and sunscreen.

Mark Birch-Machin, a skin scientist from Newcastle University, added that people must not just apply sunscreen, but make sure the amount they use is sufficient to provide protection against UVA radiation.

"Most people only apply a third to a half of the amount they need - make sure you're not one of them, especially if we have another autumn heatwave," Mr Birch-Machin told The Telegraph.