When it comes to health, scientists rarely make statements that don’t start with “maybe.” But here’s one. Excessive sun exposure causes skin cancer! There’s no “maybe” in this case. And here’s another: Chemical protection can effectively reduce exposure. But there are uncertainties when it comes to deciding which specific chemicals to use. Campaigners claim that some sunscreens are dangerous and accuse regulators of not caring about the public’s well-being, while manufacturers claim that their products have been thoroughly tested for safety and effectiveness. As usual, the public is baffled. In fact, if we put aside the unnecessary blah blah from both the alarmists and the industry, there are some simple tips. Let’s fix it.
The challenge is clear. Find a chemical or mixture of chemicals that can be applied to the skin to reduce exposure to the full spectrum of UV radiation. Then, ensure that these chemicals do not degrade upon exposure to light, have no topical or systemic toxicity, are poorly absorbed by the body, are water-resistant, have no greasy feel, are cosmetically acceptable, do not stain clothing, and can be incorporated into a “vehicle” that allows for easy delivery. A long list of requirements.
The first commercial “sunscreens” appeared in the 1960s and were designed to filter out “UVB,” the shorter wavelengths of ultraviolet (290-320 nanometers). These are the rays that cause sunburn, which was the main concern at the time. The slightly longer wavelengths, responsible for tanning, were considered safe. Finding chemicals that would absorb the harmful UVB rays was not particularly difficult, with para-aminobenzoic acid (PABA), octocrylene, phenylbenzimidazole sulfonic acid, and various cinnamates and salicylates being up to the task.
Products containing different concentrations of these ingredients have been developed for different skin types, each with a “sun protection factor (SPF),” which essentially measures how long it takes for the skin to turn red compared to no protection. The SPF value is determined in a laboratory by applying 2 mg of product per square centimeter to the skin of volunteers. Using a product with an SPF of 15 means that a person who normally starts to burn after ten minutes could theoretically stay in the sun for one hundred and fifty minutes before feeling any visible effect on their skin.
It didn’t take long for this scenario to be revealed as too simplistic. As a clear link between skin cancer and UVB became apparent, the focus shifted from sunburn prevention to skin cancer prevention, leading to an industry frenzy of products with ever-higher SPF values. In reality, an SPF of 15 already blocks 94% of UVB, just 3% less than an SPF of 30. In any case, these numbers are only meaningful if the product is applied in the same way as in the lab studies, which turns out not to be the case. Most people were applying far less than 2 mg per square centimeter and weren’t getting the protection they thought they were getting. But many of them were suffering from various skin reactions. And something else was also emerging. The longer wavelengths of ultraviolet light, 320-400 nm, known as UVA, previously thought to be harmless, have been shown to penetrate deeper than UVB and to be responsible for premature skin aging (“photoaging”). Unlike UVB, they can even pass through glass. In addition, UVA has also been shown to be potentially carcinogenic.
What was needed was a new class of products that would protect the skin from both UVB and UVA. Ideally, this would not be a product that only absorbed certain wavelengths, but one that reduced the effects of ultraviolet light through a combination of absorption and reflection. Titanium dioxide and zinc oxide, two mineral pigments, do the job, but they leave a white residue on the skin. This is fine for lifeguards’ noses, but not for swimmers’. Recently, excellent products have been developed that use “micronized” titanium dioxide and zinc oxide, which do not leave a telltale white residue. There have been concerns about titanium dioxide that has been micronized to the point of containing particles smaller than 100 nanometers, called “nanoparticles.” Ingested titanium dioxide nanoparticles can damage the genetic material of cells, but there is no evidence that these particles are absorbed through the skin. However, if they are present in spray products, inhalation could be a problem. Another problem is that when exposed to sunlight, titanium dioxide reacts with water to produce hydroxyl radicals that damage tissue. Manufacturers have solved this problem by adding chemicals such as 2-(acetoacetoxy)ethyl methacrylate that coat the titanium dioxide particles and protect them from the sun’s rays. Sunscreen needs sunscreen!
Some organic compounds like oxybenzone and avobenzone (Parsol 1789) can also absorb UVA, but oxybenzone has some drawbacks. When oxybenzone absorbs UV light, it becomes energized, and that energy is dissipated primarily through heat. But the interaction of UV light and oxybenzone can also produce free radicals that have been linked to cancer. Oxybenzone also reacts in the presence of UV light to form a compound called semiquinone, which in turn can inactivate some of the natural antioxidants found in the skin, such as reduced glutathione. This is not a good thing, since antioxidants provide protection against free radicals. And if that weren’t enough, it turns out that oxybenzone can also mimic the behavior of estrogen, at least in fish exposed to high doses. It has therefore been labeled a potential “endocrine disruptor.” Another concern about oxybenzone is that it may disrupt coral reefs.
But, and this is a big “but,” there is no evidence in the scientific literature that oxybenzone is linked to any human health problems, except for photodermatitis, a skin reaction triggered by sun exposure. There are hundreds and hundreds of compounds, both natural and synthetic, that, if examined in the same way as oxybenzone, could be linked to problems. Phthalates, bisphenol A, soy extracts, and various pesticides are estrogens. We live in a world full of hormone-like substances, and a complete blood test would reveal hundreds of them. Nevertheless, manufacturers are now reluctant to include oxybenzone in their products.
No single ingredient can protect the skin from all wavelengths of UV rays. However, a combination of avobenzone, homosalate, octosalate, and octocrylene is up to the task. The addition of tetraphalydine dicamphorsulfonic acid, known by the trade name “Mexoryl,” increases UVA protection. It is stable, absorbs UV rays, and dissipates the energy as harmless heat.
There is another “maybe” about sunscreen that has become a fact. We no longer need to claim that sunscreen can prevent skin cancer, we can claim that it does. A study in Australia, where skin cancer is a major concern, looked at 1,600 subjects who were given sunscreen to use every day for four and a half years. They developed 40% fewer squamous cell cancers than a control group who simply maintained normal skin care without any specific instructions on sunscreen use.
So, sunscreen can prevent skin cancer, which is not a rare disease. The World Health Organization estimates that 48,000 people die each year from melanoma (probably sun-related, but there is no conclusive evidence) and 12,000 from other forms of skin cancer. What can be done?
Look for a product with an SPF of at least 30. According to Consumer Reports, the best protection is a combination of avobenzene, homosalate, octosulfate, and octocrylene, found in products like Coppertone Water Baby Lotion, Walmart’s Equate Ultra Lotion, or Eucerin’s Advanced Moisturizing Lotion. Apply it 15 minutes before going out in the sun, using a shot glass full for your body and half a teaspoon for your face. Reapply frequently. Forget terms like “waterproof,” “all-day protection,” and “sweatproof.” They’re all nonsense. And if you’re buying something that’s “chemical-free,” you’re not getting a good deal because you’re buying a vacuum cleaner. Sunscreens shouldn’t be used to prolong sun exposure, but rather to protect your skin when exposure is unavoidable. Above all, remember that unfortunately there is no such thing as a healthy tan.
@JoeSchwarcz