It’s been a tough time for sunscreens recently. Earlier this year, testing on behalf of consumer organisation Choice found several sunscreens were not delivering the sun protection you’d expect. One product claimed a sun protection factor (SPF) of 50+, but when tested had an SPF as low as 4.

This triggered a series of events. Some sunscreen manufacturers paused or recalled their products. Other recalls have followed.

Media investigations have alleged issues related to how sunscreens are tested and formulated.

This week, the Therapeutic Goods Administration (TGA) said several sunscreens share a “base formula” made by a single manufacturer. It said preliminary testing had shown some sunscreens made with this base formula may be as low as SPF 4.

It’s no wonder consumers are confused about whether their sunscreens actually work.

Here’s what we know about this week’s TGA announcement and what could be behind it.

Why the concern about sunscreen SPF?

Since SPFs were introduced, they have been a clear sign for consumers about how much sun protection to expect.

But testing a product’s SPF is tricky. The usual test uses sunscreen on real people’s skin, exposes them to ultraviolet (UV) light, and checks how much redness develops over time.

Because people’s skin reacts differently, and because labs and testers vary, results can be inconsistent. For instance, products tested at one lab might show a high SPF, but might really offer much less protection when tested by another.

A sunscreen with a lower-than-claimed SPF may still offer some protection. But there would be a higher chance of sunburn, DNA damage and developing skin cancer.

What’s a base formula?

The TGA’s latest concerns relate to a “base formula” shared by several sunscreens. The base formula (also called the core or vehicle) is like the foundation of a sunscreen and includes:

• solvents/carrier liquids (water, oils, silicones)
• emulsifiers, surfactants, stabilisers (all of which allow components to blend and not separate)
• thickeners or gels
• preservatives, antioxidants
• pigments, tints, fragrances, texture enhancers.

Other ingredients are added to the base, especially UV filters. The base can also be sold to third parties with the UV filters already added. Some products include extras, such as photostabilisers to help the UV filters last longer in the sun.

The base must do several jobs well. It must:

• spread UV filters evenly (no clumps or separation)
• remain stable over time
• protect the UV filters from breaking down in the sun
• still feel good on the skin (spread easily, stick well).

Many brands use the same base and then add small differences, for instance colour or scent.

While UV filters are crucial, they cannot do their job well without a strong and well-designed base layer. So any product built on a weak or faulty base formula risks underperforming. And because many sunscreens share the same base, many products and brands can be affected.

The TGA has identified at least 21 products that use the same base formula.

How might a base formula fail?

We don’t know why the TGA is concerned about this specific base formula. But generally speaking, a base formula might fail for several reasons, including:

• poor dispersion or aggregation: UV filters can clump or settle, leaving unprotected spots
• photodegradation: without good stabilisers, filters break down in sunlight
• chemical incompatibility: additives, pigments, or fragrances may interact badly with UV filters
• dilution by inert ingredients: too much filler reduces the effective concentration of active UV filters
• physical instability: over time, the formula might separate, change viscosity, or crystallise
• manufacturing or packaging stress: insufficient mixing, exposure to heat or light during production, or poor packaging can degrade the base.

However, not every product with that base will necessarily fail. Performance of the sunscreen and subsequent protection may differ depending on ingredient tweaks, care taken during manufacture, from batch to batch, and how it’s stored.

How do I check if my sunscreen’s affected?

The TGA provides information about affected brands and products on its website, as does Choice.

Individually affected brands may publish recall notices, refund offers and batch details.

You can also contact the company with your batch number and ask if yours is affected.

What if my brand’s affected?

If your sunscreen is affected:

• don’t rely on it for sun protection, especially for long exposure
• return it to where you bought it for a refund or replacement. Some brands are offering refunds or vouchers
• watch for further TGA updates, as more products may be added to recall lists as investigations continue
• talk to a health professional if you’re worried about skin damage or past sun exposure.

What’s the take-home message?

These recent issues do not mean all sunscreens are unreliable. But they do highlight how important sunscreen design, formulation and regulatory checks are. The TGA’s investigations may even lead to stronger testing, better formulation standards, and clearer consumer guidance.

However, until we have the full picture of all brands affected, it might be wise to pick trusted brands – ones that publish test results, have transparent practices and have good reputations.

Finally, sunscreen is just one component of sun safety. Layer your defences. Also wear protective clothing, hats and sunnies, seek shade, and stay out of the sun for prolonged periods if you can.

Mike Climstein, Associate Professor, Faculty of Health, Southern Cross University; Michael Stapelberg, Adjunct Associate Professor, Faculty of Health, Southern Cross University, and Nedeljka Rosic, Senior Lecturer, Faculty of Health, Southern Cross University

This article is republished from The Conversation under a Creative Commons license. Read the original article.