The science behind reef-damaging sunscreen chemicals, and what actually works as a safer alternative.

Every summer, millions of people wade into the ocean wearing sunscreen, and most of it washes straight off. What happens after that has become one of the more uncomfortable findings in marine science: some of the most common sunscreen ingredients are quietly damaging the coral reefs we go to the beach to enjoy in the first place.

The chemicals causing the problem

It's estimated that roughly 14,000 tonnes of sunscreen enters waterways across the globe every year from both sunscreen applications and wastewater run-off.

The two ingredients with the most research behind them are oxybenzone and octinoxate, both common UV filters in conventional chemical sunscreens. A NOAA-backed 2013 study found that oxybenzone causes four distinct types of harm to developing coral: increased bleaching susceptibility, DNA damage, abnormal skeletal growth caused by hormone disruption, and outright deformities in baby coral.

The concentrations involved are strikingly small. Research has shown oxybenzone can begin damaging coral at a concentration equivalent to one drop of water diluted across six and a half Olympic swimming pools.

Is it bad to wear sunscreen in the ocean?

Hawaii's beaches have measured concentrations more than ten times that threshold, which is part of why the state banned the sale of sunscreens containing oxybenzone and octinoxate in 2018. Palau, Bonaire, Aruba, and the U.S. Virgin Islands have since passed similar restrictions.

Octinoxate carries its own separate concern: it breaks down into benzophenone, a compound flagged as both a carcinogen and a hormone disruptor. And the damage isn't limited to coral.

These same chemicals have turned up in the tissue of loggerhead sea turtles, where researchers have linked them to inflammation and oxidative stress, suggesting the impact reaches well beyond reef ecosystems alone.

Why this keeps happening even far from reefs

It's not just swimmers rinsing off at the beach. Oxybenzone and octinoxate also enter the ocean through wastewater treatment outflows, since standard sewage treatment isn't designed to filter them out.

That means the chemicals can reach marine ecosystems even from inland use, not only from sunscreen washing directly off skin in the water.

The alternatives to sunscreen

Here's an important distinction worth getting right: tallow itself has no meaningful, tested SPF.

It's a moisturising base, not a UV filter, and no peer-reviewed source supports relying on plain tallow for sun protection. The ingredient actually doing the work in any reef-safe sunscreen is a mineral active, specifically non-nano zinc oxide or titanium dioxide.

You can find our own recipe to make your own with non-nano zinc oxide powder here.

Mineral sunscreens vs chemical sunscreens

Mineral filters work differently than chemical ones. Instead of absorbing UV rays and converting them to heat the way oxybenzone does, zinc oxide and titanium dioxide sit on top of the skin and physically reflect UV rays away. Because they aren't designed to be absorbed, they don't carry the same documented coral-bleaching and hormone-disrupting effects. Non-nano zinc oxide specifically is the only UV filter permitted under Hawaii's reef-safe sunscreen law.

This is where tallow earns a real, if supporting, role. A number of small-batch sun balms now pair non-nano zinc oxide with a tallow base instead of synthetic emulsifiers and silicones.

Tallow's fatty acid profile closely resembles human sebum, so it absorbs into skin and helps the zinc spread evenly rather than leaving a thick, chalky layer. The protection comes from the zinc; the tallow simply carries it in a clean, reef-safe way.

What to check on the label

If you're switching to a reef-safer option, a few things are worth confirming before you buy:

• The active ingredient is non-nano zinc oxide or titanium dioxide, not a chemical UV filter.
• Oxybenzone, octinoxate, octocrylene, and avobenzone are absent from the ingredient list.
• "Non-nano” is stated explicitly — nano-sized mineral particles carry their own separate environmental questions.
• If SPF is claimed, it's backed by an actual active percentage and ideally lab testing, not just “estimated” figures based on the base ingredients.

The bottom line

Reef damage from sunscreen is one of the more well-documented, avoidable forms of ocean pollution, and switching away from oxybenzone and octinoxate is a meaningful, low-effort change.

Protecting your skin and protecting the reef don't have to be in competition; you just need the right ingredient doing each job.