Hits and myths: Must sunscreen have an SPF of 30+ to be truly effective?

No It's a common perception that the higher the sun protection factor (SPF), the higher the level of skin protection. Theoretically, this would be right, but the answer is not that simple, says Dr Low Chai Ling, medical director at the Sloane Clinic in Singapore.

An SPF30 product isn't twice as protective as SPF15. When applied correctly, an SPF30 sunscreen will provide only slightly more protection from UVB rays than an SPF15 sunscreen. Sunscreens with an SPF of 50 and above provide only a small increase in UVB protection.

There are two types of ultraviolet light that can harm your skin - UVA and UVB. UVA rays can prematurely age your skin, causing wrinkles and age spots. UVB rays can burn your skin. Overexposure to either can cause skin cancer. The best sunscreen offers protection from all UV light.

Dr Low says it's important to choose a broad-spectrum or full-spectrum sunscreen that is designed to protect you from both.

SPF is a measure of how well the sunscreen deflects UVB rays. Manufacturers calculate SPF based on how long it takes to sunburn skin that's been treated with the sunscreen, compared with untreated skin.

The SPF number is not the only thing to consider when trying to protect your skin from the sun. How you apply and it and how often you reapply it are also crucial. Low says that sunscreen is often not applied thoroughly or thickly enough, and it might be washed off during swimming or not reapplied on hot days when we perspire. As a result, even the best sunscreen might be less effective than the SPF number on the bottle would suggest