Why SPF Numbers Aren’t the Whole Story
Topic: Skin health
Tags: CellDerma skin health skincare spf uva uvb
Written by Dr Dev Patel BSC(HONS) MB BS DIP IMC RCS(ED) DFFP DPD MRCGP DOCCMED
SPF numbers and ratings are often misunderstood. It’s important to note that an SPF 25 product still offers very high protection, blocking just under 96% of UVB rays. By comparison, SPF 30 blocks about 96%, and SPF 50 about 97.5% — a marginal difference that is often overstated. In reality, once you exceed SPF 15 (which blocks 93%), the incremental increase in UVB protection becomes minimal. What truly matters more is how frequently the product is applied, how it performs on skin, and the quality and breadth of the protection provided.
The Limits of SPF: UVB vs. UVA Protection
SPF only measures protection against UVB rays, not UVA rays. While higher SPF numbers suggest increased sun protection, the difference is often minimal. It’s important to remember that UVA rays also damage the skin, so look for broad-spectrum sunscreens that protect against both.
Zinc Oxide
CellDerma Ultralight Mineral SPF uses zinc oxide, a mineral filter known for its exceptional broad-spectrum protection, covering both UVA and UVB rays effectively. Unlike many chemical filters, zinc oxide is also highly photostable, maintaining its protective ability over time. It works by deflecting UV radiation rather than absorbing it, offering a soothing, anti-inflammatory effect on the skin rather than the potential pro-inflammatory effects linked to some chemical sunscreens.
CellDerma Ultralight Mineral SPF uses zinc oxide, a mineral filter known for its exceptional broad-spectrum protection, covering both UVA and UVB rays effectively. Unlike many chemical filters, zinc oxide is also highly photostable, maintaining its protective ability over time. It works by deflecting UV radiation rather than absorbing it, offering a soothing, anti-inflammatory effect on the skin rather than the potential pro-inflammatory effects linked to some chemical sunscreens.
The Truth About SPF Testing
Another key issue in the SPF discussion is testing variability. Independent testing bodies — including programmes such as BBC Watchdog — have previously found that products claiming SPF 50 have, in some cases, delivered as little as SPF 5 when tested independently. There is wide variability in global testing standards. Our product is tested to stringent international protocols, and indeed, tested in a different accredited lab, the exact same formulation could easily be rated SPF 50. We chose to label it conservatively and transparently, based on our own rigorous testing.
When it comes to sunscreen, it’s not just about the number. You should always aim for SPF 30 or higher. You should also ensure your sunscreen offers broad-spectrum protection. Broad spectrum protection guards against both UVA (ageing) and UVB (burning) rays. Zinc oxide is a standout ingredient because it physically blocks UV rays by sitting on the skin’s surface and reflecting them. Unlike chemical sunscreens, which need time to absorb and become effective, zinc oxide works instantly and is typically much gentler, making it ideal for sensitive, rosacea prone or reactive skin.
Moreover, UV radiation accounts for only around 50% of the free radical activity in the skin. That’s why Ultralight goes far beyond UV protection. It includes a potent blend of antioxidants, melanin inhibitors, hydrating agents, and anti-inflammatory compounds to defend against multiple environmental aggressors and support overall skin health.
Summary
When it comes to sunscreen, it’s not just about the number. You should always aim for SPF 30 or higher. You should also ensure your sunscreen offers broad-spectrum protection. Broad spectrum protection guards against both UVA (ageing) and UVB (burning) rays. Zinc oxide is a standout ingredient because it physically blocks UV rays by sitting on the skin’s surface and reflecting them. Unlike chemical sunscreens, which need time to absorb and become effective, zinc oxide works instantly and is typically much gentler, making it ideal for sensitive, rosacea prone or reactive skin.
Top tip! The eye area is often forgotten but this is such a delicate and susceptible area and it is really important to apply SPF here. Go for products for sensitive skin that are usually tolerated well around the eye.
Ultimately, the best sun protection is one that people love using daily. The feedback we’ve received speaks volumes — users consistently tell us that Ultralight Mineral SPF feels better, performs better, and outshines the higher SPF numbers and SPF 50s they’ve used before. The proof is in the pudding. Protecting your skin is a long-term investment in your skin’s health and appearance. Apply SPF daily (even on cloudy days), reapply every two hours when outdoors, and don’t rely solely on makeup or moisturiser for sun protection. Monitor your skin regularly using the ABCDE method, and always speak to a professional if you notice changes. You can find your nearest CellDerma partnered clinic here.
