I “preach” sunscreen use to my family, friends, and patients. I do this because sunscreen helps prevent skin cancers, but in light of the recent President’s Cancer Panel report on Cancers from Environment 'Grossly Underestimated' and concerns by the group Friends of the Environment I thought perhaps I should look at the safety of the active chemicals/nanoparticles in sunscreens.
You need both UVA and UVB protection. It is the UVA rays that are most responsible for wrinkling and aging the skin. It is the UVB rays that are the most responsible for the sunburn and skin cancer formation.
According to the American Academy of Dermatology (AAD), sunscreens should ideally be water-resistant, so they cannot be easily removed by sweating or swimming, and should have an SPF of 30 or higher that provides broad-spectrum coverage against both UVA and UVB light. I think it is not worthwhile to purchase any sunscreen with an SPF higher than 55.
Remember the SPF rating only reflects the product's ability to screen or block UVB rays only. SPF 15 blocks approximately 93%of all incoming UVB rays. SPF 30 blocks 97%; and SPF 50 blocks 99%.
Active ingredients used in sunscreens:
- Avobenzone (Parsol, Eusolex, Escalol) (chemical block, UVA blocker)
- Bemotrizinol (Tinosorb S) (chemical block, UVA + UVB blocker)
- Bisoctrizole (Tinosorb M) (hybrid; UVA + UVB blocker)
- Cinoxate (chemical block)
- Ecamsule (chemical block, UVA blocker) – L’Oreal’s patented Meroxyl SX
- Octyl methoxycinnamate (octinoxate) (chemical block, UVB blocker) – potential photosensitizer
- Octyl salicylate (octisalate) (chemical block, UVB blocker)
- Oxybenzone (chemical block, UVB blocker) -- potential photosensitizer
- Sulisobenzone (chemical block, UVB blocker) – potential photosensitizer
- Titanium dioxide (physical block, UAV + UVB blocker)
- Zinc oxide (physical block, UAV + UVB blocker)
I am beginning to see physical block sunscreens called organic. I find this disingenuous as most rely on nanoparticles of Zinc Oxide (ZnO) or Titanium Dioxide (TiO2) rather than naturally found particle size. I think this is simply a marketing ploy even if “technically” true as they are both minerals.
Physical sunblockers block UV radiation mainly by reflecting/scattering the rays. They are generally insoluble and do not penetrate the skin. Zinc oxide (ZnO) and titanium dioxide (TiO2) nanoparticles used in sunscreens range in the 20 – 30 nm size. Their use has become popular as the nanoparticles appear transparent when applied to the skin rather than as a thick opaque white cover. This transparency makes the sunscreen much more cosmetically acceptable than the larger-particle ZnO and TiO2 use.
The physical and chemical properties of nanoscale materials, such as reactivity, persistence, or bioavailability, can differ significantly from their larger scale counterparts. This is the concern of the group Friends of the Earth who feel that sunscreens with nanoparticles are a risk to your health and urge you not to use them.
While the FOTE quote a recent Australian study by Macquarie University's Professor Brian Gulson as evidence that sunscreens using nano-ZnO are potentially hazardous due to absorption into the blood stream through the skin, Gulson in an interview notes that his study doesn't shed any light on the question of whether the nano-particles themselves played a part in the zinc absorption. “That was the most critical thing. This isotope technique cannot tell whether or not it's a zinc oxide nano-particle that got through skin or whether it's just zinc that was dissolved up in contact with the skin and then forms zinc ions or so-called soluble ions. So that's one major deficiency of our study.”
Other studies not mentioned by FOTE suggest the case for safe, non-penetrating, transparent, topical ZnO sunscreen formulations appears to be strengthening as the one by Sheree Cross and colleagues.
Chemical sunblocks work mainly by absorbing UV light. Most are synthetic chemicals that are soluble in oil and/or water. Many can penetrate the skin at least to some degree.
The useful ability of chemical sunblocks to absorb UV light is also a potential source of harmful effects as some can actually be responsible for photosensitization leading to sun damage rather than protection. Often this is what is happening when someone says “I’m allergic to sunscreen.”
Not all chemical sunblocks are created equal. For example, ecamsule (Mexoryl SX), homosalate and a few others appear to have a relatively good safety profile. On the other hand, such agents as octocrylene, octinoxate, oxybenzone and sulisobenzone appear to be more damaging. If choosing a chemical sunscreen formula, examine the list of ingredients and look up the information (on this site and elsewhere) on the specific blockers used in the formula.
The chemicals used in sunscreens as with many skin care ingredients have not been researched to the possibility of low-level topical or systemic toxicity with long-term use.
A concern in the use of nanoparticles and chemicals in sunscreens is the exposure of the body due to oral and nasal uptake due to application to the lips and mouth area, around the nose, and via contact with sunscreened hands themselves or with handling food.
Philip Moos and colleagues looked at the effects of nanomaterials in the colon. Their experiments used cell cultures of colon cells to compare the effects of zinc oxide nanoparticles to zinc oxide sold as a conventional powder. They found that the nanoparticles were twice as toxic to the cells as the larger particles. This is a study of cell cultures which now needs to be looked at again in living gut before getting too concerned. The scientist also not that the concentration of nanoparticles that was toxic to the colon cells was equivalent to eating 2 grams of sunscreen — about 0.1 ounce.
While the final word may not be out on the safety of nanoparticles and chemical in sunscreens at this point I feel safe in using them and recommending their use to family, friends, and patients. No sunscreen is recommended for oral consumption, so care should always be used in washing your hands prior to eating.
Lips are an area commonly involved in skin cancer formation, so it is important to protect them. When using sunscreen lip balm, don’t lick your lips. This will reduce the accidental ingestion of any potentially harmful chemicals, nanoparticle or not.
If you are worried about chemicals or nanoparticles in sunscreens, then use other sun safe practices:
- Staying in the shade, especially between the sun’s peak hours (10 a.m. - 4 p.m.).
- Covering up with clothing, a brimmed hat and UV-blocking sunglasses.
- Avoiding tanning and UV tanning booths.
Sunscreens should not be used in babies under 6 months old. It is recommended by the American Academy of Pediatrics for this group to use other sun safe practices such as the ones just mentioned.
When you do use sunscreens, use at least an SPF 15 and preferably one with a sunblock component also. To protect against the UVA rays, the product needs to have avobenzone (Parsol 1789), ecamsule (Mexoryl), titanium dioxide, or micro-zinc oxide.
- Apply the sunscreen 20-30 minutes before going outside. Reapply every two hours when outside at a beach, etc. for adequate protection.
- Use enough. To ensure that you get the full SPF of a sunscreen, you need to apply 1 oz – about a shot glass full.
- Reapply after getting out of the water or toweling off. Even "water-proof" sunscreens are not usually "towel-proof".
- Use even on a cloudy day, up to 80% of the sun's ultraviolet rays can pass through the clouds. In addition, sand reflects 25% of the sun's rays and snow reflects 80% of the sun's rays.
- Don't forget to apply lip balm with SPF 15 or higher.
Don’t forget you can check out the Environmental Working Group’s list of the best and worst sunscreens can be found on their searchable database. A few of the best rated include: Al Terrain Aquasport Performance SPF 30, Badger Sunscreen for Body and Face SPF 30, California Baby Sunscreen SPF 30, and Vanicream Sunscreen Sport SPF 35.
Facts About Sunscreens; American Academy of Dermatology
Food and Drug Administration: Sun Protection; Rulemaking History for OTC Sunscreen Drug Products
Friends of the Earth: Nanosunscreens Threaten Your Health
Human Skin Penetration of Sunscreen Nanoparticles: In-vitro Assessment of a Novel Micronized Zinc Oxide Formulation; Sheree E. Cross, Brian Innes, Michael S. Roberts, Takuya Tsuzuki, Terry A. Robertson, Paul McCormick; Skin Pharmacol Physiol 2007;20:148–154; DOI: 10.1159/000098701
ZnO Particulate Matter Requires Cell Contact for Toxicity in Human Colon Cancer Cells; Philip J. Moos, Kevin Chung, David Woessner, Matthew Honeggar, N. Shane Cutler and John M. Veranth; Chem. Res. Toxicol., 2010, 23 (4), pp 733–739; DOI: 10.1021/tx900203v
The Dermatology Blog: Sunscreens Cause Skin Cancer? What?! (June 1, 2010)