Sunscreen is only needed if you're going to be under direct sunlight The straight answer: No The facts: Sun exposure is one of the primary causes of premature skin ageing, not to mention skin cancer. Yet, how many of us bother applying sunscreen - not just to our face but our body as well - before heading out? You might think that you don't need to wear sunscreen if you are not going to be exposed to the sun for an extended amount of time. But even being indoors all day, or being outside when the sky is cloudy, can have damaging effects on your skin. The sun emits UVB and UVA rays, both of which are detrimental to the skin. According to Dr Low Chai-ling, a dermatologist and medical director at The Sloane Clinic in Singapore, UVB rays are like long nails that can quickly puncture your car tyres and ruin your ride. These rays are the most problematic, and are responsible for skin darkening, wrinkles, free radical production, DNA damage and cancer. UVA rays, on the other hand, are like small nails that cause minimal damage that can build up over time. UVA rays are less problematic than UVB rays in the short-term, but they are longer than UVB rays, and this is dangerous in the long-term. Not protecting yourself from these rays can still age and darken your skin, as well as put you at risk of developing DNA damage and cancer. "Don't save the sunscreen only for sunny days," Low says. "Even when it's cloudy, up to 80 per cent of the sun's ultraviolet rays can pass through the clouds and damage your skin. Also, sand reflects 25 per cent of the sun's rays, while, in the case of snow, that figure is 80 per cent." Being in your house, car or office all day can also have an adverse effect on your skin if you do not protect it with sunscreen. Window glass in buildings and cars, for example, only protects you from UVB rays, letting in 62.8 per cent of UVA rays that can damage your skin. You are not safe with tinted windows, either, as ordinary tinting only blocks 3.8 per cent of UV rays. Fluorescent lighting can also produce small amounts of UV rays that can be damaging over time, adds Low. Sitting under these lights - or even near a window where you may be exposed to the sun's UV rays - can lead to skin damage. This means that you need to protect yourself, whether that means tinting your windows, covering the window, or wearing sunscreen all the time. Says Low: "I always tell my patients to apply sunscreen every day to their exposed skin, whether or not they are going to be in the sun. On days when they are going to be indoors, I advise them to apply sunscreen on areas not covered by clothing. "Sunscreen can be applied under make-up, or, if you prefer the fuss-free route, there are many cosmetic products, such as foundation and face powder, that contain sunscreen. Sun protection is the principal means of preventing premature skin ageing and skin cancer. "It's never too late to protect yourself from the sun, and in doing so, you minimise your future risk of skin cancer."