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

PUBLISHED : Tuesday, 15 October, 2013, 12:00am
UPDATED : Monday, 16 December, 2013, 1:11pm

Must sunscreen have an SPF of 30+ to be truly effective? The straight answer: No The facts: 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

There are other points to consider when choosing a sunscreen, says Low: sunscreens contain filters that reflect or absorb UV rays. There are two main types, organic and inorganic. Also called chemical sunscreens, organic sunscreens absorb UV radiation and convert it to a small amount of heat. This group of active ingredients is the most widely used in sunscreens. Organic sunscreens might contain avobenzone, cinoxate, ecamsule, menthyl anthranilate, octyl methoxycinnamate, octyl salicylate, oxybenzone or sulisobenzone. Inorganic sunscreens are also called physical sunscreens and they reflect and scatter UV radiation. Inorganic sunscreens might contain titanium dioxide or zinc oxide. Most broad-spectrum sunscreens use both ingredients to better block UVA and UVB rays.

Water-resistance is also important. Sunscreens that pass a water-resistance test can be labelled "water-resistant" for either 40 or 80 minutes, as long as they also include instructions to reapply after 40 or 80 minutes of swimming or sweating, after towel drying and at least every two hours.

"Choose a broad-spectrum sunscreen of at least SPF30 for daily use," Low says. "If you are going to be in water, get one that is water-resistant. To achieve the SPF reflected on a bottle, use about 2mg of sunscreen per square centimetre of skin. This translates to applying the equivalent of a shot glass (two tablespoons) of sunscreen to the exposed areas of the face and body - a good-sized dollop to the face alone. If you are using a spray, apply until an even sheen appears on the skin."

Remember, sunscreen needs to be reapplied every two hours, or more frequently after swimming, heavy perspiration, or towelling dry. The SPF should be 15 or higher for adequate protection and, ideally, 30 or higher for extended time spent outdoors. Also seek shade whenever possible, and wear sun-protective clothing, broad-brimmed hats, and UV-blocking sunglasses.