When choosing sunscreen, it’s easy to assume that SPF 50 must offer twice as much protection as SPF 30. After all, 50 is almost double 30. But sunscreen ratings don’t work that way.
SPF 50 provides more protection than SPF 30, but it isn’t twice as effective. The difference is smaller than many people realise.
SPF stands for Sun Protection Factor. It measures how effectively a sunscreen protects the skin from UVB radiation - the type of ultraviolet radiation primarily responsible for sunburn. In New Zealand, sunscreens are tested and labelled according to the New Zealand Sunscreen Standard, AS/NZS 2604.
The SPF number is based on the amount of UVB radiation that reaches the skin when sunscreen is applied correctly under laboratory conditions.
So, while SPF 50 provides a higher level of protection, the difference is around one percentage point - not double the protection.
The remaining UVB exposure may sound small, but even a modest increase in protection can be helpful - particularly considering most people also apply less sunscreen than is needed to achieve the protection shown on the label. Applying too little sunscreen can significantly reduce the level of protection you receive.
No. A higher SPF does not mean you can stay in the sun for twice as long or wait longer before reapplying.
Both SPF 30 and SPF 50 need to be applied generously and reapplied according to the product instructions. Sunscreen can wear off through sweating, swimming, toweling off and general movement, regardless of its SPF rating.
For the best results, apply sunscreen generously to clean, dry skin before heading outdoors. Reapply regularly, particularly after swimming, sweating or toweling off.
SPF mainly tells you about protection from UVB radiation. It does not provide the full picture of protection against UVA radiation, which can contribute to premature skin ageing, long-term skin damage and skin cancer.
For everyday use, choose a sunscreen labelled ‘broad spectrum’. This means it provides protection against both UVA and UVB radiation.
Yes. SPF 30 provides a high level of protection when it is applied correctly and reapplied as directed. SPF 50 offers very high protection, but neither sunscreen blocks every UV ray.
The most important sunscreen is one you will use properly and consistently. If you prefer the feel, finish or price of an SPF 30 product, using it generously every day is likely to provide better protection than applying a small amount of SPF 50.
Sunscreen is also only one part of a complete sun-protection routine. When UV levels are high, combine sunscreen with protective clothing, a broad-brimmed hat, sunglasses, shade and avoiding direct sun where possible.
Southern Cross Affiliated Provider for eligible treatment services at select clinics
