Sunscreen Science 101: Understanding what’s in your sunscreen

In Australia, sunscreen is practically a reflex. Whether it’s a beach day, a morning jog, or a quick walk to the café, we’ve been taught to slather up before stepping outside. Most of us trust the SPF number on the bottle to keep us safe under our famously strong sun, but recent findings from the Therapeutic Goods Administration (TGA) suggest there’s more to the story.

The TGA reviewed a range of sunscreens and found that some didn’t quite meet their labelled SPF claims. While that might sound alarming, the issue wasn’t poor manufacturing, it was about the science of formulation and the importance of robust testing. Sunscreen performance depends on two key factors: the active UV filters that provide protection, and the base formula that helps those ingredients stay evenly spread and stable on your skin.

In short? Ingredients matter and so does how they’re put together.

Understanding SPF and Broad-Spectrum Protection

SPF, or Sun Protection Factor, measures how well a sunscreen protects against UVB radiation, the kind that causes sunburn. An SPF 30 filters about 97% of UVB rays, while SPF 50 filters about 98%. That’s only a 1% difference, showing that higher numbers don’t necessarily mean dramatically better protection.

However, SPF doesn’t cover UVA rays, which penetrate deeper and contribute to premature ageing and long-term skin damage. That’s where broad-spectrum protection comes in. Under 2021 Sunscreen Standard, therapeutic sunscreens must protect against both UVA and UVB to make the claim that they are broad-spectrum.

Achieving that balance relies on the careful selection and combination of UV filter ingredients. So, while SPF tells part of the story, broad-spectrum coverage is the full chapter.

UV Filters Explained

Sunscreens rely on UV filters, active ingredients that absorb, reflect, or scatter ultraviolet light. These fall into two categories:

• Mineral filters such as zinc oxide and titanium dioxide, and
• Chemical filters like avobenzone, Tinosorb S, Tinosorb M, and Uvinul T 150.

Here’s what they do:

• Zinc oxide offers broad-spectrum coverage, blocking both UVB and UVA, including the deepest UVA1 wavelengths. It’s highly photostable, meaning it maintains protection even after prolonged sun exposure.
• Titanium dioxide provides excellent UVB and UVA2 protection. It is often paired with zinc oxide to fill gaps in spectrum coverage, especially in formulations that prioritise a lighter feel.
• Avobenzone absorbs UVA rays but needs stabilising to stay effective in sunlight. Modern formulations often use Tinosorb S to help maintain avobenzone’s stability and extend its protective effect.
• Tinosorb S (Bemotrizinol)and Tinosorb M (Bisoctrizole) are next-generation filters that cover both UVA and UVB. They’re extremely photostable and help stabilise other filters in a formulation, improving both SPF performance and longevity.
• Uvinul T 150 (Ethylhexyl Triazone) is a strong UVB absorber that adds protection with good photostability.

By combining several UV filters, formulators can create sunscreens that are both broad-spectrum and stable, meaning they deliver reliable protection for longer. In fact, Australian standards require that broad-spectrum sunscreens maintain a minimum level of UVA protection relative to their SPF, a goal achievable only through well-designed ingredient combinations.

Why the “Base” Formula Matters

A sunscreen’s base formula is like its foundation; it holds the active UV filters in place and helps them spread evenly across your skin. If that base isn’t stable, the filters can clump or separate, meaning the product may not deliver the protection it promises.

The TGA’s recent review has found that some underperforming sunscreens shared a base formula that couldn’t consistently deliver SPF 50+ protection. The active ingredients were present but weren’t being distributed effectively. The review also raised concerns about overseas lab testing, highlighting the need for validated, reliable methods.

Bottom line? Strong protection depends on both a well-built formula and accurate testing.

Choosing Smart: How to Read a Sunscreen Label Like a Pro

As a health-conscious consumer, you don’t need a chemistry degree to make an informed sunscreen choice. Here’s what to look for:

• Broad-spectrum protection: This ensures UVA and UVB coverage, as required under Australian standards.
• Recognisable, evidence-backed UV filters: Ingredients like zinc oxide, titanium dioxide, or stabilised avobenzone. Tinosorb S or M, Uvinul A Plus are often listed under their chemical names Bemotrizinol, Bisoctrizole, and Ethylhexyl Triazone.
• TGA-listed products: In Australia, sunscreens are regulated as therapeutic goods to ensure their quality, safety and efficacy.
• Reapplication guidance: Even the best sunscreen needs to be reapplied every two hours, after swimming, sweating and towel drying.

The Bottom Line

Stay calm and sunscreen on! The TGA’s sunscreen review is a good thing and reminds us that sun protection is a science, not just a number on a bottle. A high SPF is only part of the equation; smart formulation, regular reapplication, and sun-safe habits like wearing protective clothing are what truly keep your skin safe.

And the good news? Our WholeLife Pharmacy and Health foods team is across the latest developments, so you can feel confident knowing you’re getting up-to-date, evidence-based advice. Whether you’re choosing a sunscreen, checking ingredients, or just wondering what “broad-spectrum” really means, we’re here to help you make informed, skin-smart choices under the Aussie sun.

References:

1. 1. Sunscreens using the same base formulation as Ultra Violette Lean Screen SPF 50+ sunscreen (2025). Therapeutic Goods Administration (TGA). https://www.tga.gov.au/products/medicines/sunscreens/sunscreens-using-same-base-formulation-ultra-violette-lean-screen-spf-50-sunscreen
   2. Echo Hui et al., (30 Sep 2025). ABC News. More sunscreens pulled from shelves over SPF concerns. https://www.abc.net.au/news/2025-09-30/more-sunscreens-pulled-from-shelves-over-spf-concerns/105836976
   3. Sunscreen SPF testing – information for consumers. (16 Sep, 2025)  Therapeutic Goods Administration (TGA). https://www.tga.gov.au/news/news/sunscreen-spf-testing-information-consumers.
   4. Gabros, S., Patel, P., & Zito, P. M. (2025, March 28). Sunscreens and Photoprotection. Nih.gov; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/sites/books/NBK537164/
   5. Updates to the Sunscreen Standard. (2022, June 21). Therapeutic Goods Administration (TGA). https://www.tga.gov.au/how-we-regulate/supply-therapeutic-good/supply-non-prescription-medicine/non-prescription-medicine-requirements-and-standards/manufacturing-requirements-and-standards-non-prescription-medicines/standards-non-prescription-medicines/updates-sunscreen
   6. Burkhart CG., (2022). Safer and More Broad-spectrum Ultraviolet Protective Sunscreens. Open Dermatology Journal. http://dx.doi.org/10.2174/18743722-v16-e2208110
   7. INCIDecoder. Ingredient data entries for Tinosorb S, Tinosorb M, Uvinul A Plus. Cosmed Sun Essential Lotion ingredients (Explained)