Are chemical sunscreen filters safe?

Where the fear came from, what the research shows, and why Cloudwear uses one.

Written by Dr. Aimee Paik, MD, board-certified dermatologist and VIZE co-founder

In short

Chemical sunscreen filters picked up a bad reputation in part from a regulatory status that sounds worse than it is. What you need to know is that the FDA hasn't found them harmful, it’s just asked for more data because unlike zinc oxide and titanium dioxide, chemical filters can be systemically absorbed. The studies that measured that absorption used far more sunscreen than anyone actually wears, and where researchers have looked for hormone effects, they've turned up only at concentrations not possible to reach in real daily use for most chemical UV filters.

Filters 101, and where the fear started

Every sunscreen works through filters. Mineral filters, zinc oxide and titanium dioxide, absorb, reflect and scatter UV. They're white by nature, which is what causes the white cast you sometimes see with mineral sunscreens. Chemical filters, sometimes called organic filters, absorb UV and are transparent by nature. Some sunscreens use only mineral filters, others use only chemical filters. Hybrid sunscreens use a combination of both. 

Here's what most people don't know: in the US, sunscreen is regulated as a drug, not a cosmetic. Every filter has to be on an FDA-approved list before a brand can put it in a bottle, and that list was written decades ago.

In 2019, and then again in 2021, the FDA set out to update it, holding every filter to modern safety standards. Zinc oxide and titanium dioxide cleared. The FDA's term for a cleared filter is GRASE, which stands for generally recognized as safe and effective. A couple of older filters were designated as “not GRASE,” but those filters had already been phased out of the US market and were no longer in use. Everything else, including most chemical filters, landed in a third category: not enough data yet.

That third category is where the confusion lives. A filter still under review is technically not “GRASE," which sounds an awful lot like "not safe." But that’s not what it means, it means the file is still open, and more data is being gathered. While it's open, those filters stay on the market.

To find out whether these filters could move into GRASE, the FDA ran absorption studies. The point of the study was to determine when you put sunscreen on your skin, do the filters end up in your blood? If the answer was yes, more data would be needed before the FDA could make a determination. 

Participants applied sunscreen at 2 mg/cm² across 75% of their body, which is roughly everything a bathing suit doesn't cover. They applied this once the first day, and then four times a day for the next 3 days. Blood was drawn throughout and measured against a 0.5 ng/mL threshold.

That 0.5 ng/mL mark (the amount of sunscreen filter present in the bloodstream) was selected to be an extremely cautious threshold below which no further testing is needed because the level is that low. It translates to less than one-half of one part per billion. If a filter shows up above it, the FDA's rules require more safety testing before that filter can be cleared. It doesn't mean anything harmful was found.

And then there’s the application amount. At my height and weight, using the study protocol’s calculation method, this works out to 24 grams of sunscreen per application, which is roughly half a tube of Cloudwear, with 13 applications total in four days. This translates to the equivalent of almost six-and-a-half full tubes of Cloudwear over a four day period! It takes a truly Herculean effort to apply that much sunscreen, and I’m a dermatologist. Most people underapply, often using less than a quarter to half the recommended amount, and feel good about reapplying even once or twice throughout the day.

When researchers measured maximum blood levels, most filters showed up in the blood at single-digit levels, but one filter didn’t behave like the others. Oxybenzone measured in the hundreds. 

What about the claim that chemical filters disrupt hormones?

Endocrine disruption means interfering with hormones, mainly sex, thyroid and adrenal. That sounds really scary, but let’s dive into the data and find out what it really means. 

Researchers ran chemical UV filters through large screening programs that test whether a substance can nudge hormone systems. Six common chemical filters showed some signal of weak hormone activity: octisalate, homosalate, octocrylene, avobenzone, octinoxate, and oxybenzone. But "some signal in a lab dish" is not the same as "disrupts hormone signals in your body." 

Most activity only showed up above cell-killing doses. For all of these filters except one, the hormone activity only appeared at concentrations so high they were already poisoning and killing the cells. When cells are dying, the test readouts get scrambled, so any hormone signal isn't trustworthy evidence of a real hormonal effect.

The doses were higher than anything your skin absorbs. Scientists compared the doses that triggered lab effects against the highest amounts these filters can be absorbed, which were determined by the maximum usage trials we already discussed above. For most of the UV filters, the amount required to trigger weak endocrine signals was 100-fold higher than maximum absorption amounts. 

Here's where a lot of the fear actually started.

To test whether something behaves like estrogen, researchers use two classic setups. They add it to breast cancer cells that are known to multiply in response to estrogen and watch whether the cells grow. Or they give it to rats and see whether the uterus gets heavier, which is what estrogen does. If either happens, the substance is acting like a hormone.

Some chemical filters did produce those effects, and those studies are behind most of the headlines you've seen. But the doses required were 20 to 500 times greater than your body could ever absorb from sunscreen. Factor in how much sunscreen people actually put on, and the gap gets wider still. Those two dose ranges could never possibly overlap. 

A comprehensive review concluded that avobenzone, ensulizole, homosalate, octinoxate, octisalate and octocrylene show no estrogenic activity at concentrations relevant to how sunscreen is actually used.

The one real exception: oxybenzone

Oxybenzone, also called BP-3, is different from the other chemical filters. Your body also breaks it down into a second compound, BP-1, which shows estrogen activity at levels people could potentially reach. Two things set oxybenzone apart.

1. Its hormone activity showed up at doses that weren't harming the cells.

In the screening assay described above, every other filter's signal only appeared at cell-killing doses, which is exactly why those results can't be trusted. Oxybenzone's turned up while the cells were still alive.

2. It absorbs into the body at far higher levels than the other filters.

In the FDA's absorption study, most filters showed up in blood at single-digit concentrations. Oxybenzone measured in the hundreds. Safety comes down to the gap between two numbers: the dose that caused an effect in the lab, and the most your body could realistically absorb. For the other filters, that gap is so wide, they could never overlap in the real world. For oxybenzone, it's closer to 1.5 to 6 times. 

Another note that makes oxybenzone different from other chemical filters, is that it isn't only used in sunscreen. It's used as a UV stabilizer in makeup, hair products, fragrance, food packaging, plastics, and textiles. So exposure can add up from many directions. 

Luckily, oxybenzone has largely been phased out of most US sunscreens. While there are a few sunscreens that still use this UV filter, they are hard to find. 

Why Cloudwear uses octinoxate

We chose 7.5% octinoxate to work with our 10.15% proprietary zinc oxide, adding UV protection while keeping the formula light.

Octinoxate is one of the most efficient UVB absorbers available, which means less total filter is needed to reach the SPF we wanted. That's what makes Cloudwear light, non-greasy, and free of a typical sunscreen smell.

It also holds up on the safety data. Octinoxate shows no hormone activity at maximal blood concentrations, and it has an established safety and regulatory track record across decades of use worldwide. 

The one thing it comes with is Hawaii. Octinoxate is one of the two filters the state restricted, so Cloudwear can't be sold there. That restriction came out of legislation rather than a testing standard, which is a distinction worth understanding. [We wrote about what "reef safe" actually means here.]