Ah, summer – the best season of the year. Days at the beach, evenings in the park, rooftop parties and backyard barbecues. Sunny warmth giving us healthy doses of vitamin D.
Unfortunately, the sunny rays we love also pose a risk: skin cancer. There are three major types of skin cancer, with melanoma being the most serious. In the United States alone, the incidence of melanoma has been increasing about 3% each year in non-Hispanic Caucasians, and it is estimated that 1 in 37 men and 1 in 56 women will develop melanoma in their lifetimes.
Ultraviolet (UV) exposure from sunlight is a high risk factor for melanoma. UV categorized into UV A, B, and C, with B considered the most dangerous because it has the smallest wavelength and highest energy.
Thankfully, we have sunscreen to help us out. Sunscreen either absorbs or reflects UV rays (depending on the type used), preventing them from reaching our skin. Additionally, some sunscreens contain nanoparticles of titanium dioxide (TiO2), which have a very high refractive index for UV and therefore further shield us from the damaging radiation. However, there’s some controversy regarding the safety of these nanoparticles, and whether they are themselves carcinogenic. Are the ingredients in sunscreen harmful as well as helpful? These concerns captured the media’s attention in a recent New York Times article.
Hopefully the following information can shed some light on the matter.
To start out, let’s get a grasp of how UV light rays cause cancer in the first place. UV light has the ability to penetrate our cells and reach DNA, and when it does , it can cause damage to our DNA in the form of small breaks. Our cells are faced with DNA damage regularly and have efficient repair mechanisms. But if a cell has more damage than the repair machinery can handle, mutations may accumulate in critical parts of our genome, leading to uncontrolled cell growth: a tumor. An important part of melanoma initiation is also UV-induced inflammation, which is a marker of tumor growth.
Here’s how titanium dioxide comes into the picture: the fear is that TiO 2 in sunscreen can penetrate the skin and lead to inflammation, causing the exact effects we were trying to avoid. Let’s address each of these problems.
Titanium dioxide nanoparticles are between 1 and 150 nanometers. Particles of any material smaller than 1 micrometer can penetrate the skin, so these nanoparticles can theoretically be absorbed. In real life, though, it’s not clear whether this happens. The World Health Organization reports that a human study in which patients applied sunscreen with TiO 2 for up to a month didn’t show increased concentrations of TiO 2 in the skin. Other studies demonstrated a build-up on the uppermost layer of skin, but no further penetration. These studies may not have been carried out for sufficient amounts of time or with enough number of people -- only 13 patients were tested -- so it’s still possible that titanium dioxide can be absorbed by skin and that the proper study just hasn’t been done yet.
Here’s another kink, though: even if TiO 2 does get absorbed, application of titanium dioxide to the skin still doesn’t seem to be that dangerous. Experiments that applied titanium dioxide to the skin of mice for several days did not result in any inflammation or other detectable adverse effects.
What’s the risk, then? Why is it classified as a potential carcinogen by the World Health Organization?
It turns out that the problems caused by titanium dioxide were noticed not after skin application, but upon inhalation and ingestion. A single dose of TiO 2 given intranasally to mice led to inflammation, and mice given TiO 2 in drinking water started showing genetic damage after 5 days. This seems to indicate that lotion sunscreens might be okay, but spray-on sunscreens could be bad news.
We can try to estimate our TiO 2 exposure from spray-on sunscreen: most sunscreens have about 0.5 mg TiO 2 per gram. Proper coverage requires 2 mg sunscreen per cm2 of skin, and the average person has 1.8 square meters of surface area. This corresponds to 36 g of sunscreen and 18 mg TiO 2 . An initial application will typically last about 2 hours, so let’s say on average we’d be exposed to 9 mg TiO 2 per hour. The recommended exposure limit for TiO 2 dust is 1.5 mg per cubic meter of air, and an average breathing rate of 0.3 cubic meters of air per hour would be equivalent to 0.45 mg inhaled TiO 2 per hour. For an application of spray-on sunscreen to be less than this amount, we’d have to inhale 5% or less of what is sprayed. Keeping the spray away from your face is a good start, and switching to lotion-based sunscreen is probably better.
Our bodies don’t have a way to effectively remove titanium dioxide, so anything that is inhaled will likely stay in our system for many years. The small size of these particles also means that they could reach other organs. To truly determine the long-term risk of titanium dioxide exposure, comprehensive studies will need to be done looking at multiple types of cancer, not just melanoma or lung cancer.
If you, like me, tend to take a better-safe-than-sorry approach and would like to check your sunscreens for titanium dioxide, here is a list of trade names it may be classified under:
Aeroxide, A-Fil Cream, Atlas white titanium dioxide, Austiox, Bayertitan, Calcotone White T, Comet, Cosmetic White C47–5175, Cosmetic White C47–9623, C-Weiss 7, Flamenco, Hitox, Hombitan, Hombitec, Horse Head A-410, Horse Head A-420, Horse Head R-710, Kemira, KH 360, Kronos titanium dioxide, Levnox White RKB, Pretiox, Rayox, Runa RH20, Rutile, Rutil RC, Rutiox, Tichlor, Tiofine, TiO 2 Hombitan, Tiona T.D., Tioxide, Tipaque, Ti-Pure, Ti-Select, Titafrance, Titan, Titania, Titandioxid, Titanium White, Titanox, Titanox 2010, Trioxide(s), Tronox, Tytanpolr, Unitane products (various), UV-Titan, 1700 White and Zopaque
Have a happy and safe summer! And don’t eat or inhale your sunscreen.
To check out some of the research for this post and the WHO report, see the links below: