The past few years have seen an explosion of skin care products labelled as "natural" or "organic". In many cases, these products claim to be healthier, safer and more effective, and whether they truly are or not is an important question for consumers. Sun creams marketed as "natural" are often mineral sunscreens that contain only the ultraviolet filters titanium dioxide and zinc oxide. While both titanium dioxide and zinc oxide are naturally-occurring, they are heavily processed and refined for use in sunscreens, making the term "natural" somewhat misleading.
In scientific terms, the mineral ultraviolet filters are known as physical filters. They are inert metals that sit on the skin and absorb, scatter or reflect light (in contrast to chemical filters such as avobenzone or octocrylene that work by absorbing light and converting it to heat). Physical filters have the advantage of being gentle, stable (they are not degraded by sunlight) and nonallergenic. Their disadvantage rests with the fact that zinc oxide is less efficient than the chemical filters; ounce for ounce, it generally provides a lesser degree of protection, and so larger quantities of it need to be used in a formulation. Depending on the percentage used and the size of the sunscreen particles, physical filters may also leave a white cast, and there is some concern that this, along with the thick texture of many mineral sunscreens, may discourage some from applying these products as liberally as is needed to provide adequate protection.
The lower efficiency of some mineral sunscreens has been illustrated by Consumer Reports. Each year, they independently test dozens of sunscreens sold on the US market for their UVB and UVA protection, as well as for water resistance. An analysis of four years of their data found that only 26% of the "natural" sunscreens tested met their SPF claims (in contrast to 58% of "chemical" sunscreens). One of the sunscreens they tested claimed an SPF of 50 and registered an SPF of 8, and none of the "natural" sunscreens they tested scored highly enough to make their recommended list.
Like all things in life, sunscreens are not created equal, regardless of whether they contain largely mineral or chemical filters, and blanket statements suggesting that "mineral sunscreens are better" are inaccurate and dangerous. The debacle involving the Honest Company's sunscreen last year illustrates this point. The company came out with a product that contained 9.3% zinc oxide and no other active ingredients. It was heavily marketed, carried by major retailers, and endorsed by the Environmental Working Group. SPF testing had been done by a private company, and the product had been deemed to have an SPF of 30 (which is isn't possible for a product that contains only 9.3% zinc oxide and no other sunscreen active ingredients). It wasn't long before reports emerged of individuals developing severe sunburns after having used the sunscreen, and the company now faces class action lawsuits over the issue. To their credit, they have since more than doubled the amount of zinc oxide in their sunscreen, but the point remains that buyers must beware when choosing their sun-protection products.
Whether one should choose a mineral sunscreen versus one that largely uses chemical filters really depends not only on the active ingredients a sunscreen contains, but also on the circumstances in which a sunscreen is used, its such that there isn't a "one-size-fits-all" answer. A mineral sunscreen with an effective SPF of 15 may work reasonably well in Canadian fall, winter and spring, but may not protect from harmful sunburns when used at the beach in the Caribbean. In general, a well-formulated "chemical" sunscreen will provide a higher degree of protection than most mineral sunscreens, and may be a better choice in times of high-intensity sun exposure.
In my opinion, a well-formulated mineral sunscreen is often a good choice for young children (over 6 months...those under 6 months should be kept out of the sun), and for children with eczema or sensitive skin. Research has also shown that physical and chemical UV filters complement each other, such that some sunscreens that combine zinc oxide and/or titanium dioxide with chemical UV filters perform well. If you choose to use a mineral sunscreen, I recommend looking for one with a high SPF and applying it generously. For better protection from longer UVA rays, choose a product that contains zinc oxide alone (in high concentrations of at least 16-18%), or zinc oxide in combination with titanium dioxide.
Both mineral and "chemical" sunscreens have advantages and disadvantages, but mineral products may be more likely to provide a lesser degree of protection than they advertise, creating a challenge for consumers who prefer to use this type of product. When choosing a sunscreen, the Skin Cancer Foundation and Canadian Dermatology Association websites are good places to start. Both organizations maintain lists of sunscreens that have been vetted by their respective teams of scientists and/or doctors. Choose your product wisely and enjoy the outdoors this summer!