{"id":260826,"date":"2025-10-02T11:00:24","date_gmt":"2025-10-02T01:00:24","guid":{"rendered":"https:\/\/www.russh.com\/?p=260826"},"modified":"2025-10-02T10:23:54","modified_gmt":"2025-10-02T00:23:54","slug":"sunscreen-spf-variance","status":"publish","type":"post","link":"https:\/\/www.russh.com\/sunscreen-spf-variance\/","title":{"rendered":"How is it possible for SPF ratings to vary across the same product?"},"content":{"rendered":"

It’s not an easy time to be a sunscreen customer in Australia. From the recent Choice report into some of Australia’s most popular sunscreens, to the recent change in legal levels of ingredients like oxybenzone<\/a> and homosalate, and now news that even more sunscreens have been pulled from shelves, sifting through all of the information to get answers is arduous. But, the Therapeutic Goods Administration maintains that all sunscreens in Australia are indeed safe and you shouldn’t lose trust in sunscreens. Particularly not when Australia has the highest rates of melanoma in the world.<\/p>\n

There are some explanations as to why SPF ratings on the same product can vary from test to test. But the key take away is to always put your sun protection first \u2013 a sunscreen that you are happy to apply correctly will be more likely to protect you than one you don’t like to use. Here is what you need to know about how and why sunscreen testing results can vary.<\/p>\n

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Human error in assessing the test results<\/h3>\n

Did you know that assessing the SPF of a sunscreen all comes down to the human eye<\/a>?<\/p>\n

Sunscreen is applied to a subject’s skin, which is then put under a UV light. Human testers then look at the skin and assess how long it takes to turn pink or burn. Despite the strict rules around this testing process \u2013 which even dictate the colour of the walls in your testing room \u2013 this is not an exact science. The opinion of one tester can vary from the opinion of another.<\/p>\n

The good news is that a better testing method could be on the way. A method of in vitro evaluation of sunscreens<\/a> could be on the way soon. Many experts believe this method of testing could have increased accuracy<\/a>. Although there is still debate within the scientific community on this point.<\/p>\n

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Product stability issues<\/h3>\n

Lab Muffin Beauty Science created an informative video<\/a> that explains how and why stability issues in sunscreen formulas can occasionally happen, particularly in the mineral or zinc sunscreen space.<\/p>\n

First, let’s look at why someone might choose a mineral sunscreen. Many people who turn to mineral sunscreens do so because they have delicate, sensitive or acnes-prone skin. Zinc is naturally healing, its an ingredient used to treat burn victims, it’s also used in nappy rash and barrier creams.<\/p>\n

Unfortunately, it is difficult to formulate with zinc oxide, because it doesn’t naturally mix with water, and it’s easier to stabilise in oil<\/a>. Zinc is also thick and often leaves a white cast on its wearer.<\/p>\n

This presents a problem. A formula that mixes and stabilises zinc with oil is not always the preference for those with acne-prone or sensitive skin. Manufacturers who set out to create a product that sensitive-skin users will actually want to apply have a tricky road to navigate. Finding a way to stabilise a zinc-based formula that is wearable, water-based and appropriate for sensitive is not always easy. And even currently stable products can become unstable when left in cabinet for years.<\/p>\n

This is why we tend to see higher variances in SPF testing across mineral sunscreens compared to chemical sunscreens. According to Lab Muffin Beauty Science<\/a>, the age of the sunscreen, storage, batch and other factors could all affect stability and change the SPF of a sunscreen. This is why one bottle could have a higher SPF than another bottle of the same formula.<\/p>\n

Does this mean all mineral sunscreens are bad? Of course not. Chemical sunscreens are not absolved of stability issues, and its not the case that all mineral sunscreens are unstable. Formulation issues are outliers. Australian sunscreen testing is very strict and the TGA maintains that sunscreens sold in Australia are safe<\/a>.<\/p>\n

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Application issues or other human error<\/h3>\n

In order to get the SPF written on the bottle of your sunscreen, you have to apply the recommended amount of sunscreen. You also have to apply the sunscreen with enough time for it to dry down and form a protective laye<\/a>r.<\/p>\n

If you don’t apply the correct amount, or use the product outside of the directions on the bottle, you will not see the same SPF compared to when you use the product as directed.<\/p>\n

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What can you do as a consumer?<\/h3>\n

Lab Muffin Beauty Science science gave some advice<\/a> on sunscreens she thinks you could set aside for now. She says that if you have seen any sunscreens with a rating that you are concerned about, you should treat all sunscreens with the same ingredient levels and formulations with equal caution.<\/p>\n

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