Chemicals in sunscreens are absorbed into the human body at levels high enough to raise concerns about potentially toxic effects

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For years, you’ve been urged to slather on sunscreen before venturing outdoors.

But new U.S. Food and Drug Administration data reveals chemicals in sunscreens are absorbed into the human body at levels high enough to raise concerns about potentially toxic effects.

Bloodstream levels of four sunscreen chemicals increased dramatically after test subjects applied spray, lotion and cream for four days as directed on the label, according to the report.

The levels far exceed the FDA-set threshold which require topical medications to undergo safety studies, said Dr. Kanade Shinkai, a dermatologist with the University of California, San Francisco School of Medicine.

“It’s not like they went a little bit over,” she said. “It’s really quite high, orders of magnitude higher than that.”

However, experts are quick to say you shouldn’t stop using sunscreen because of this study.

At this point, the known risk of harm from the sun’s rays exceeds the potential risk posed by these chemicals.

“I am concerned that people are going to stop wearing sunscreen,” Shinkai said. “We know ultraviolet light from the sun has very deleterious effects on the skin.

It causes photoaging. It causes sunburn.

And, as such, it causes melanoma and [other] skin cancer.”

Dr. Michele Green, a dermatologist with Lenox Hill Hospital in New York City, agreed.

“I think it’s confusing,” Green said.

“While it’s more than the FDA recommends for their toxicology, we really don’t know what that means in terms of human health. I would not want people to stop using sunscreen based on this one study.”

Possible effects on hormones

The sunscreen study was led by the FDA’s Dr. David Strauss, and appears May 6 in the prestigious Journal of the American Medical Association, one of the nation’s leading medical journals.

Most sunscreens on the shelf use chemicals such as oxybenzone, avobenzone and octocrylene to block harmful rays.

These organic chemicals absorb ultraviolet radiation and convert it into a small amount of heat.

However, animal studies have raised concerns that the chemicals, oxybenzone in particular, might disrupt normal hormone patterns in people, the FDA researchers noted in their study.

“These molecules are chemical rings, essentially, and they absorb light,” said Shinkai, who co-wrote an editorial accompanying the study.

“Chemical rings are also the fundamental basis for a lot of hormones, and chemical rings tend to enter cells.”

Oxybenzone has been found in human breast milk, amniotic fluid, urine and blood, the FDA researchers said.

For its study, the FDA randomly had 24 adults apply either a sunscreen spray, lotion or cream four times a day for four days.

The participants applied the sunscreen to three-quarters of their body surface.

The study took place in a lab, and the agency drew 30 blood samples from each participant over a week to see whether the chemicals in the sunscreen got absorbed through the skin.

Levels of oxybenzone, avobenzone, octocrylene and ecamsule increased in the bloodstream after sunscreen use, researchers found.

“There is definitely reason for concern, because if you think about it, any medication you buy over the counter, you would expect that everything in there has been tested, it’s safe, it’s effective,” Shinkai said.

‘This has never been proven for sunscreen.”

More real-life data needed

But it was a very small-scale laboratory study that simply shows the need for more research, said Dr. Raman Madan, a dermatologist with Northwell Health’s Huntington Hospital in Huntington, N.Y.

“While this is a starting point, the relevance of this result is unknown,” Madan said. “There needs to be further studies done to show what this really means. While it could have real-world consequences, it could very well mean nothing.”

The study also differs from real life in that people applied the sunscreen while hanging about a lab, Shinkai said.

“They weren’t doing the things people typically do when they use sunscreen,” such as swimming or working in the yard, Shinkai said.

Because of this, their exposure might differ from that of everyday people.

The Consumer Healthcare Products Association (CHPA), a group representing sunscreen makers, also said it’s far too soon for consumers to have doubts about these products.

“Sunscreen manufacturers, FDA, and dermatologists are aligned on the goal of protecting the public from the harmful effects of the sun,” the group said in a statement. “Sunscreens save lives.”

CHPA said the FDA is committed to learning more about the safety of chemicals within sunscreens, however, and the new data “is consistent with these efforts.”

Options are out there

The FDA has been tussling with sunscreen manufacturers over studies to test the safety of their products, said Shinkai.

The agency has set a November 2019 deadline for manufacturers to provide safety data on their sunscreens, including evaluations of systemic absorption, the risk of cancer from the chemicals, and their effect on reproductive health, Shinkai said in her editorial.

The publication of this study might be intended to put pressure on the sunscreen industry to meet the deadline, she said.

“The FDA is a regulatory agency. It’s not a testing agency. For them to perform a research study is highly unusual,” Shinkai said. “I think that’s an important thing that suggests how concerned they were about this issue, and maybe perhaps the frustration on their part.”

People who are concerned about the safety of chemical sunscreens can opt to use mineral sunscreens, Shinkai said.

Those sunscreens rely on zinc oxide and titanium dioxide to reflect sunlight from the skin, rather than absorbing it like chemical sunscreens.

“These we know are safe,” Shinkai said of mineral sunscreens. “This is something that is evidence-based.”

BUT……. These are myths and are not backed by research or chemical knowledge.

Inorganic vs. Organic

In marketing, organic is a label that describes how something is produced – often with a safe-list of chemical treatments and approved practices.

In chemistry, organic means the chemistry of compounds that contain carbon. Titanium dioxide and zinc oxide don’t contain carbon. They’re made up of metal and oxygen and classified as inorganic.

Marking the categories as organic and inorganic makes more sense because all of the sunscreen chemicals used contain carbon, except for titanium dioxide and zinc oxide.

SunscreenChemical FormulaComposition
Zinc OxideZnO1 Zinc + 1 Oxygen
Titanium DioxideTiO21 Titanium + 2 Oxygens
OctocryleneC24H27NO224 Carbons + 27 Hydrogens + 1 Nitrogen + 2 Oxygens
AvobenzoneC20H22O320 Carbons + 22 Hydrogens + 3 Oxygens
OctinoxateC18H26O318 Carbons + 26 Hydrogens + 3 Oxygens

Organic and inorganic is also a useful way to categorise sunscreens because the way that the carbon atoms are linked up in organic sunscreens is why they absorb UV energy. If you look at the chemical structure of an organic sunscreen like avobenzone you’ll see that they have single bonds alternated with double bonds.

avobenzone

This alternation or conjugation of the single and double bonds allows the molecule to absorb energy along the electromagnetic spectrum. The amount of conjugation determines which part of the electromagnetic spectrum they absorb, whether that be in the visible spectrum to produce a colour, or in the ultraviolet spectrum to protect our skin from UV.

uv-color-spectrum

Inorganic and organic neatly divide the two sunscreen types and are also descriptive. I know most companies won’t want to confuse their customers by labelling their 80% organic-certified sunscreen product with titanium dioxide as inorganic, but at least as sunscreen shoppers we can understand the difference!

Myths about using Inorganic vs Organic Sunscreens

“Inorganic sunscreen and organic sunscreens work differently”

Mostly Myth! It’s often said that inorganic sunscreens (titanium dioxide and zinc oxide) reflect UV off of the skin and organic sunscreens absorb UV and convert it into heat. In reality, for most of the UV spectrum they work very similarly.

Organic sunscreens absorb UV because of the way the bonds between their carbon molecules are arranged. The number of bonds between the carbon atoms in the sunscreen molecules and their conjugated arrangement give sunscreens their absorptive properties in the UV region of the electromagnetic spectrum. Remember that conjugated means alternating single and double bonds!

The energy from UV light promotes electrons in the conjugated carbon bonds of organic sunscreen molecules from a lower energy state to a higher energy excited state. The excited electrons in the bonds then relax or release the absorbed energy by stretching, vibrating, or bending – this turns that energy into heat.

In some cases, the organic sunscreen chemical can’t relax and release the absorbed energy by bending, stretching, or vibrating and the absorbed energy causes a change in its structure. This is what happens with avobenzone, it absorbs the UV energy and instead of relaxing, it changes its structure – and this new structure formed from avobenzone doesn’t absorb UV energy as well. As more and more avobenzone molecules’ structures change, the less UV energy is absorbed by the sunscreen formula. Some of the new structures formed from avobenzone are also more irritating and sensitising to the skin. Photo-stabilizers prevent this from happening by absorbing the energy from excited avobenzone and releasing it before its structure can change.

Inorganic sunscreens work very similarly – even though their structure is different from organic sunscreens. Metal oxides, like titanium dioxide and zinc oxide, have solid structures made of alternating sheets of metal and oxygen atoms. The principle behind the UV protection is exactly the same as organic sunscreens. Instead of the arrangement and amount of carbon bonds, the particle size of the titanium dioxide or zinc oxide determines which parts of the electromagnetic spectrum it absorbs.

There is a strong belief that these inorganic metal oxide sunscreens act by reflecting UV light instead of absorbing it, but this isn’t the complete story. UV light is divided into UVB and UVA. UVB is between 280 to 315 or 320 nm and UVA is between 315 or 320 to 400 nm. Inorganic sunscreens predominately absorb in the UVB spectrum and reflect in the long UVA (above 360 nm) and visible spectrum. Only about 5% of UVB light is reflected by inorganic sunscreens and the remainder gets absorbed and converted – just like organic sunscreens.

The results of a measurement show how much energy is reflected by different types and sizes of titanium dioxide. The horizontal scale represents the electromagnetic spectrum with my yellow highlight marking the UV spectrum. The vertical scale represents how much of the energy is being reflected, the higher up on the chart – the greater the amount of reflection.

titanium dioxide2

Between 250 nm and 350 nm titanium dioxide reflects less than 10% of the energy. Between 350 nm and 400 nm there is more reflection depending on the form of titanium dioxide and the particle size. The anatase form of titanium dioxide exhibits more reflection than the rutile form of titanium dioxide. These forms have to do with the way the titanium and oxygen atoms are arranged in the titanium dioxide. Sunscreens often use rutile titanium dioxide because they are safer and less reactive.

The same is seen with zinc oxide, with most of the reflection being above 350 nm. The rest of the UV spectrum is absorbed.

zinc oxide

The high reflection above the UV spectrum (above 400 nm) into the visible light region of the electromagnetic spectrum is what causes the whitening effect and flashback when using inorganic sunscreens.

“You can use less of an inorganic sunscreen compared to an organic sunscreen”

Myth! All sunscreens are tested at the same density, which is 2 milligrams of sunscreen per square centimetre. That applies to inorganic, organic, spray, stick, lotion, wipes, etc.

If you want to get as close as possible to the protection on the label of the sunscreen product, you need to apply it at the same density it was tested at.

“Inorganic sunscreens sit on the skin. Organic sunscreens absorb into the skin”

Myth! Think of it this way, if we want to protect ourselves from the rain we need to hold the umbrella above our heads. Sunscreens work the same way, you want them to absorb the energy before they can reach our skin cells, particularly the living cells. The most effective way for this to be done is to have them on the surface of the skin in a continuous and even layer.

Both organic and inorganic sunscreen particles can penetrate into the upper layers of the skin. If and how much they penetrate is dependent on properties like their particle or molecular size as well as the overall sunscreen formula. This isn’t a desired effect and formulators work to reduce the amount that penetrates. Modern organic sunscreens often have larger molecular sizes, chemical and physical properties, or even coatings which make it more difficult for them to penetrate past the surface of the skin.

Keep in mind that skin penetration doesn’t mean that it’s causing harm to our bodies. There has to be a biological mechanism for it cause an effect. There is a lot current and ongoing research into this area, but we don’t have any strong answers yet.

“Inorganic sunscreens provide protection right away. Organic sunscreens need to activate on the skin”

Myth! Organic sunscreens and inorganic sunscreens absorb UV due to their electronic properties. There’s no activation or chemical reaction that occurs on the skin with organic sunscreens to create photoprotection.

We know this is true because we can measure how much UV is absorbed by an organic sunscreen off of the skin, like on a piece of clear plasticOrganic sunscreens will also prevent UV colour changing bracelets, beads, or stickers from changing colour.

Both inorganic and organic sunscreens will provide UV protection as soon as they’re placed on the skin. The reason why a wait time is part of the application instructions is to allow the sunscreen formula time to dry and form a film on the skin. This makes it harder for it to be wiped off and it also means it can dry to as even of a film on the skin as possible.

The more evenly distributed the sunscreen is on the skin, the more even the coverage and the greater the average protection. If we take 10 umbrellas and hold them over one person, that one person may remain very dry during a downpour but everyone else will get soaked – if we distribute the umbrellas evenly more people will remain dry. Photoprotection works the same way, it’s measured as an average – you don’t want some areas of the skin with more sunscreen and greater coverage at the expense of other areas with less sunscreen and less coverage.

“Inorganic sunscreens don’t need to be reapplied”

Myth! All sunscreens should be reapplied if you want to maintain photoprotection throughout the day. While it’s true that titanium dioxide and zinc oxide don’t change structure under normal UV radiation, that’s true for many organic sunscreens and sunscreen formulas as well.

The reason why reapplication is recommended is because we often don’t apply enough in the first place and it’s constantly being removed from our skin. Reapplication helps ensure that we have a minimum density of 2 milligrammes per square centimetre of sunscreen on our skin and that we maintain that density throughout the day.

We may not be conscious of removing our sunscreen, but touching our skin, putting on and taking off clothing, using our phones, sweating, eating…all these things will remove some of the sunscreen from our skin. Think about how the coverage of a foundation or lipstick changes throughout the day.

There is no clear answer as to when you should reapply your sunscreen. We all do different things throughout the day in regards to our skin, so the amount of sunscreen removed from the skin will differ from person-to-person and day-to-day. That’s why it’s difficult to have a single rule that will apply to everyone. Conclusions from studies vary in their recommendations for when and how often to reapply.

What you choose to do is up to you, but you should take into account how much UV you’re exposed to, how much you expect to be exposed to, and your activities. You should think about reapplying your sunscreen before going for a jog outdoors. Work in an office? Maybe reapply before you leave the office. What’s clear though is that you should definitely reapply after sweating, swimming, bathing, and abrasion (like laying on sand) – even if you are using a water-resistant sunscreen.

In the UK many sunscreens are marketed as ‘once-a-day’, but health organisations recommend disregarding that and still reapplying throughout the day.

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