Reef-safe sunscreens

Two types of ultraviolet (UV) rays from the sun reach the Earth’s surface. Both are harmful. Long wave UVA light penetrates our skin causing wrinkling and sunspots. Short wave UVB light mostly attacks our outer layer of skin leading to sunburn and tanning. Both cause skin cancer.

Public health advice worldwide recommends liberal use of a broad spectrum sunscreen, for protection from both UV types. For decades, aside from complaints over greasy textures and the staining of a few clothes, the reputation of sunscreens has remained remarkably clean. ‘It’s a lifesaver’, has been the official government message.

In the past couple of years, however, the tide of legislative opinion has started to turn. This follows growing concerns that some of the popular sunscreen ingredients may be damaging coral reefs.

Thousands of tons of sunscreen end up in our oceans each year, much of it washed off our skin as we enjoy a dip in the sea. Recent research has indicated that some of the chemicals these products contain can then be absorbed by corals doing harm such as causing bleaching. Governments are starting to act.

On 1 January 2020, the Pacific island of Palau will become the first country to ban all sunscreens that contain any one of ten chemicals. In the US, a year later, bans on sunscreens containing two chemicals will come into force in the state of Hawaii and the city of Key West in Florida. The Caribbean island and Dutch municipality of Bonaire has similar legislation pending.

The naughty list

Only four of the chemicals being banned in Palau have UV protecting properties: oxybenzone, octinoxate, octocrylene and 4-methyl-benzylidene camphor. Some antimicrobials and preservatives are also on the list. Oxybenzone and octinoxate are also being banned in parts of the US.

The UV protectants facing bans are all organic molecules that absorb UV rays and convert them into a small amount of heat. There is a second category of active sunscreen ingredients, inorganic molecules, which mostly block or reflect UV radiation instead. Zinc oxide and titanium dioxide are the two most frequently used.

The inorganic ingredients tend to be less popular with consumers as they can leave behind a white coating and be harder to rub in. Nano-sized versions of these minerals overcome some of the issues, but come with their own (different) environmental concerns.

So what are ‘reef-friendly’ active sunscreen ingredients? That’s a hard question to answer. An added complication here is that some researchers believe there isn’t sufficient evidence yet that the organic molecules on the naughty lists are actually harmful at the concentrations and conditions seen in the wild. Most of the research so far has been done in the lab.

Lessons from nature

Most manufacturers are using larger, non-nano particles of zinc oxide and titanium dioxide in sunscreens marketed as reef-friendly. Others are reaching for natural organic molecules. ‘Nature already has many good solutions for protecting organisms from UV damage,’ explains Yousong Ding, an assistant professor of medicinal chemistry at the University of Florida in Gainesville, US. Yousong is focusing his attention on the natural product shinorine, which is already used in a couple of commercially-available sunscreens.

A number of marine organisms, including marine algae and cyanobacteria, produce shinorine to shield themselves from solar damage. ‘These marine organisms cannot move but are consistently exposed to UV damage,’ Yousong says. ‘Shinorine is how they protect themselves.’ Currently, it is extracted from a type of red algae harvested from the wild, which limits the volume available for sunscreen production.

Yousong is keen to use his biotechnology know-how to develop a more reliable production method that can be used on a larger scale. ‘Shinorine sunscreen products are not widely available, you can’t grab them from grocery stores or supermarkets yet,’ he explains. Yousong hopes to change this.

The chemists inserted the genes responsible for the natural synthesis of shinorine in the cyanobacterium Fischerella into another – faster growing – strain of cyanobacterium, Synechocystis. Yousong’s engineered cyanobacterium produces shinorine in just a few weeks, compared to the year needed with the red algae. ‘We are interested in working with some companies about the possibility of using our production method commercially,’ he says.

Adding a protective layer

Not all natural UV protectants are suitable for using in sunscreen formulations. Dutch researchers have been working with the consumer goods manufacturer Unilever on a way to circumvent this, by coating them in natural polymers.

Encapsulation prevents the active molecules from coming into direct contact with the skin, which has several advantages, explains Arnout Imhof, an associate professor of soft matter at Utrecht University in the Netherlands. It protects the molecules from degradation, caused by oxygen or other chemicals in a sunscreen formulation, and also protects the skin from any irritation from the molecules.

Quercetin, retinol and p-coumaric acid are the three natural products that Arnout chose to encapsulate. ‘Together these absorb the complete UV part of the spectrum,’ he explains. His team were able to successfully coat these in both ethyl cellulose, a derivative of cellulose, and the protein zein, from the maize plant.

Time will tell whether Arnout’s or Yousong’s approaches will make it out of the lab and onto the shelves. But with the bans starting to be enforced in the next couple of years, the future is looking bright for any sunscreen able to put reef-friendly on its label.