Sunscreen myth directory | Lab Muffin Beauty Science

Here’s a growing directory of resources on sunscreen myths. They’re written as truths instead of myths, except where explicitly called out. These are mostly secondary sources, by me or other science communicators – most cosmetic science studies need to be interpreted with nuance to be useful.

Also check out this sunscreen FAQ, and my Basic Skincare Guide eBook which goes through how to choose and use a sunscreen, as well as cleanser and moisturiser.

Sunscreen safety

All sunscreens are actually very safe

Chemical sunscreens (oxybenzone, octocrylene etc.) are very safe. They’re some of the most closely scrutinised ingredients in consumer products. 

Mineral nanoparticles are also very safe. The nanoparticles do not go past the dead skin layers on intact skin.

US FDA regulations

The FDA has not declared that chemical sunscreens are no longer safe – there is a proposed change in their GRASE status due to lack of data. This is intended to be a call for companies to provide data, in which case their GRASE status will be maintained. This is currently in limbo due to animal testing bans. However, the same chemical sunscreens have been confirmed to be safe in the rest of the world through other methods, such as in the EU.

Studies by the FDA found that chemical sunscreens absorbed into the blood, but this doesn’t mean they’re unsafe. The amounts were minuscule, and just meant more data was required for them to maintain their GRASE status. 

Endocrine disruption

“Potential endocrine disruptor” doesn’t mean something will disrupt your hormones to any significant extent. In the context of cosmetic ingredients, it usually means it’s been found to bind weakly to hormone receptors in test tube studies.

It’s very unlikely that low doses of chemical sunscreens can have a harmful endocrine-disrupting effect (commonly referred to as “non-monotonic dose response effects” or NMDR – you might also see this myth stated as “the dose does NOT make the poison for endocrine disruptors”). 

Benzene contamination in sunscreens wasn’t dangerous 

Benzene was found in some sunscreens (both chemical and mineral) in 2021 by Valisure, a laboratory involved in class action lawsuits and not known for accurate measurements. Even with their likely inflated numbers, the amounts of benzene in sunscreens were not expected to cause any noticeable health effects.

Sunscreens aren’t bleaching coral reefs

This was mostly based on a single dodgy study published in 2016 that was heavily promoted in the media (“science by press release”). A comprehensive 400 page review by the National Academies in 2022 found that  mineral and chemical sunscreens have overlapping environmental impacts – mineral sunscreens aren’t clearly better for the environment, by any measure. The report concluded that sunscreen bans were “premature” and not based on good data, and cited the NOAA “Skincare Chemicals and Coral Reefs” page as an example of poor communication.

Sunscreen ingredients

Mineral sunscreens don’t reflect much UV

Mineral sunscreens mostly (90-95%) work by absorbing UV and converting it to heat, just like chemical sunscreens. Mineral sunscreens aren’t more effective, or safer for melasma, because of this.

SPF boosters

If a “100% mineral” sunscreen isn’t too whitening, it probably contains hidden chemical sunscreens (SPF boosters). These are almost identical to chemical sunscreens, but for esoteric regulatory reasons, don’t need to be listed in the active ingredients. They’re as safe as chemical sunscreens, but can cause reactions if you’re allergic.

Photostability

Avobenzone doesn’t need to be avoided in sunscreens due to its lower stability – it can be stabilised very effectively, such as in Neutrogena’s Helioplex formulas which retain 85% of UVA protection after 5 hours of midday equivalent sun.

Allergies

Roughly 1% of people are allergic to chemical sunscreens, not 25%. 

Using sunscreen

Chemical sunscreens don’t react with skin to work

Chemical sunscreens don’t need to absorb into skin, or react with skin, to work. They don’t need to be applied to bare skin, and should be applied OVER skincare, just like mineral sunscreens.

Chemical sunscreens work immediately. The wait time (usually 15-20 min) is for all sunscreens, to let them dry down and not smear off, and ensure you don’t expose your skin to UV while applying.

Sunscreen amount

There isn’t a set number of “fingers” of sunscreen to use on your face, since the size of these “fingers” varies a lot. To get the labelled SPF you need to apply 2 milligrams of product per square centimetre of skin (the amount used in testing). 1/4 teaspoon (1.25 mL) is a good, generous guideline for most people’s faces.

Do you need sunscreen?

Australia has the most up-to-date, evidence-based sun exposure guidelines that balance the benefits and risks of sun exposure. The latest version (2023) even takes into account skin tone. Most people should take sun protective measures (including wearing sunscreen) for skin cancer prevention purposes on days when the UV index is forecast to reach 3 or over.

Sunscreen reapplication

Most sunscreens are very photostable now. The reason for reapplication is usually not decomposition of ingredients due to UV exposure – it’s usually the sunscreen film clumping up and wearing off over time.

Labels: SPF, PA etc.

SPF testing is standardised around the world

SPF is tested in pretty much the same way regardless of region. Most regions use the ISO 24444 method which involves human volunteers and a UV lamp, or a slightly modified version. This means “SPF 30” on an Australian sunscreen is not higher than on any other sunscreen, and it’s not tested differently to take into account Australia’s higher UV levels.

SPFs over 30 are good

SPF 50 is significantly more effective than SPF 30, not just 1% more effective. SPF 30 only blocks 97% of erythemal (reddening) UV and SPF 50 only blocks 98% when the full amount is applied perfectly evenly. Inadequate and imperfect application means more UV gets through. This is the biologically relevant UV, and the ratio will match the SPFs (i.e. SPF 50 will let through 3/5 of the amount SPF 30 does) if the same amount of sunscreen is used.

You can’t work out SPF rating from the percentages of the active ingredients. Factors like how the ingredients are distributed in the sunscreen, any SPF boosters in the formula etc. will alter the protection of the final film.

Sunscreen product types

Sunscreen sprays and mists don’t give much protection. Only around 1/5 to 1/9 of a sunscreen sprayed at your face from 20 cm away will land on your skin (for the sunscreens I tested, you’d need to apply roughly 80-120 sprays to achieve the labelled SPF on your face).

Sunscreen sticks

Sunscreen sticks require a lot of passes to give adequate protection. The common recommendation of 4 passes doesn’t seem to be valid for current sticks – the 3 sticks I tried needed 34 passes on average to achieve the labelled SPF.

SPF lip products

SPF lip products are safe – they’re tested for oral use, including if you swallow some.

Blue light

Blue light from the sun causes longer lasting tanning in darker skin tones

Mineral sunscreens don’t protect against blue light

Tinted products protect from blue light

Digital screens don’t emit enough blue light to worry about. You don’t need to wear sunscreen in front of the computer, for example.