Are sunscreens always beneficial, or can they be detrimental to users? A research team led by UC Riverside chemists reports that unless people out in the sun apply sunscreen often, the sunscreen itself can become harmful to the skin.
When skin is exposed to sunlight, ultraviolet radiation (UV) is absorbed by skin molecules that then can generate harmful compounds, called reactive oxygen species or ROS, which are highly reactive molecules that can cause "oxidative damage." For example, ROS can react with cellular components like cell walls, lipid membranes, mitochondria and DNA, leading to skin damage and increasing the visible signs of aging.
When sunscreen is applied on the skin, however, special molecules -- called UV filters -- contained in the sunscreen, cut down the amount of UV radiation that can penetrate the skin. Over time, though, these filters penetrate into the skin below the surface of the epidermis, the outermost layer of skin, leaving the body vulnerable to UV radiation.
Led by Kerry M. Hanson, a senior research scientist in the Department of Chemistry at UCR, the researchers report that three UV filters (octylmethoxycinnamate, benzophenone-3 and octocrylene), which are approved by the Food and Drug Administration and widely used in sunscreens, generate ROS in skin themselves when exposed to ultraviolet radiation, thus augmenting the ROS that is naturally produced. The researchers note that the additional ROS are generated only when the UV filters have penetrated into the skin and, at the same time, sunscreen has not been reapplied to prevent ultraviolet radiation from reaching these filters.
Study results will appear in an upcoming issue of Free Radical Biology & Medicine. An advance copy of the paper is available online on the journal's Website.
"Sunscreens do an excellent job protecting against sunburn when used correctly," said Hanson, who works in the laboratory of Christopher Bardeen, an assistant professor of chemistry at UCR. "This means using a sunscreen with a high sun protection factor and applying it uniformly on the skin. Our data show, however, that if coverage at the skin surface is low, the UV filters in sunscreens that have penetrated into the epidermis can potentially do more harm than good. More advanced sunscreens that ensure that the UV-filters stay on the skin surface are needed; such filters would reduce the level of UV-induced ROS. Another solution may be to mix the UV-filters with antioxidants since antioxidants have been shown to reduce UV-induced ROS levels in the skin."
In their research, Hanson and colleagues used epidermal model tissue and applied sunscreen to the surface to test the effect of sunscreen penetration on ROS levels in the deep epidermis. A two-photon fluorescence microscope allowed them to visualize ROS generation occurring below the skin surface. The ROS activity was detected using a probe molecule whose fluorescent properties change upon exposure to ROS. On comparing images taken before and after the skin was exposed to UV radiation, they found that ROS generation in the skin increased after sunscreen penetration.
About 95 percent of the visible signs of aging are associated with UV exposure. About 90 percent of a person's total life-time UV exposure is obtained before the person is 18 years of age. Only a few UV-filters are available that block "UV-A," the wavelengths that penetrate more deeply into the skin, all the way into the dermis where collagen exists.
"For now, the best advice is to use sunscreens and re-apply them often -- the Skin Cancer Foundation recommends every two hours, and especially after sweating or swimming, which can wash away sunscreen -- to reduce the amount of UV radiation from getting through to filters that have penetrated the skin," Bardeen said. "This, in turn, would reduce ROS generation."
Next, the researchers plan to investigate the effect of smog on ROS generation in the skin.
Besides Hanson and Bardeen, Enrico Gratton in the Laboratory for Fluorescence Dynamics, UC Irvine, collaborated on the study. The research was funded by grants from the National Science Foundation and the National Institutes of Health.
Which Sunscreens Are The Safest?
By Dr. Mercola - 6/6/2011
The Environmental Working Group's 2011 sunscreen guide can help you determine which sunscreens are unsafe. The group recommends just 20 percent of the 600-plus sport sunscreens it evaluated.
For a product to score high marks, it needed to be free of potentially harmful chemicals. Not surprisingly, their list of products to avoid list contains some popular brands.
EWG's Sunscreens To Avoid:
- Aveeno Active Naturals Hydrosport Sunblock Spray, SPF 85
- Aveeno Sunblock Spray, Continuous Protection, SPF 70
- Banana Boat Kids UltraMist Sunscreen, SPF 110
- Banana Boat Kids UltraMist Sunscreen, SPF 85
- Banana Boat Sport Performance Active Max Protect Continuous Spray Sunscreen, SPF 110
- Banana Boat Ultra Defense UltraMist Sunscreen Continuous Clear Spray, SPF 85
- CVSExtreme Sport Clear Mist Sunscreen Spray, SPF 70+
- CVS Sheer Mist Sunscreen Spray, SPF 70
- Neutrogena Fresh Cooling Sunblock Lotion, Body Mist, SPF 70
- Neutrogena Spectrum+ Sunblock Spray, SPF 100
- Neutrogena Ultimate Sport Sunblock Spray, SPF 100+
- Neutrogena Ultimate Sport Sunblock Spray, SPF 70
- Neutrogena Ultra Sheer Body Mist Sunblock Lotion, SPF 100+
- Neutrogena Ultra Sheer Body Mist Sunblock Lotion, SPF 70
- Neutrogena Wet Skin Kids Sunblock Spray, SPF 70
- Neutrogena Wet Skin Sunblock Spray, SPF 85+
- Walgreens Sheer Body Mist Sunscreen, SPF 70
How did EWG come up with this list? Each of the products to avoid meets all of these criteria:
SPF values above 50-plus. Higher SPF products are not necessarily best. In fact, the Food and Drug Administration says these numbers can be misleading. There's a concern that high SPF products may give people a false sense of security and encourage people to stay out in the sun for too long without reapplying sunscreen. It's also important to note that the SPF is based solely on UVB protection. Sunscreen sprays. They can fill the air with tiny particles that may not be safe to breathe in, according to EWG. Contains oxybenzone and vitamin A. Oxybenzone is a concern because it penetrates the skin, is associated with allergic reactions, and is a potential hormone disruptor. Retinyl palmitate is a form of vitamin A that may not be safe when exposed to sunlight. EWG recommends choosing products with one of these ingredients instead: zinc, titanium dioxide, avobenzone, or Mexoryl SX.
Which products does EWG recommend? Here's a list of its best beach and sport sunscreens.
Unfortunately, some of the safest and most effective sunscreens on store shelves can be expensive so it's worthwhile to shop around for deals. Here are the most affordable products that performed well in EWG's ratings (calculated by Yahoo! based on price per ounce).
Safer, Affordable Sunscreens:
- Alba Botanica Sun: Mineral Sunscreen Fragrance Free, SPF 30
- Alba Botanical Sun: Mineral Sunscreen Kids, SPF 30
- Aubrey Organics Natural Sun Saving Face Sunscreen, SPF 15
- All Terrain Aquasport Performance Sunscreen, SPF 30
- All Terrain KidSport Sunscreen, SPF 30
- BabyGanics Cover Up Baby Sunscreen for Face & Body, Fragrance Free, SPF 50+
- Carribean Solutions Natural/Biodegradable SolGuard, SPF 25
- Carribean Solutions Sol Kid Kare Natural Sunscreen, SPF 25
- Earth's Best: Sunblock Mineral Based, SPF 30+
- Goddess Garden Kids Natural Sunscreen, SPF 30+
- Goddess Garden Natural Sunscreen, SPF 30+
- Jason Natural Cosmetics Sunbrellas: Mineral Natural Sunblock, SPF 30
- Johnson & Johnson's Baby Daily Face & Body Lotion, SPF 40
- Mexitan Products Sunscreen Lotion, SPF 50 and SPF 30
- MelanSol Natural Sunscreen for Face and Body, SPF 25
- Nature's Gate Mineral Sportblock, SPF 20
- Purple Prairie Botanicals SunStuff, SPF 30
- Solbar Zinc Protection Cream, SPF 38
- Sunbow Dora the Explorer Pink Sunscreen, SPF 30
- Tropical Sands All Natural Sunscreen, SPF 50 and SPF 30
- Vanicream Sunscreen for Sensitive Skin, SPF 30
- Vanicream Sunscreen Sport, SPF 35
EWG also includes ratings for best moisturizers, lip balms, and makeup with SPF.
It's worth noting that using sunscreen is only one part of smart sun protection. Limit your time outside in the middle of the day when the sun's rays are most intense. Wear a hat, sunglasses, and protective clothing (dark and tightly-woven). Get more sun safety tips from EWG.
This Is A Partial List Of Carcinogenic Ingredients That Are Found In Many Sunscreen Lotions:
- Aminobenzoic Acid - carcinogen implicated in cardiovascular disease.
- Avobenzone - carcinogen
- Cinoxate - evidence of skin toxicity
- Dioxybenzone - strong evidence of skin toxicity and carcinogen; hormone disruptor and has been found in waterways, soil and air. Has been shown to have a "gender bender" effect in animals
- Diazolidinyl Urea - carcinogen, endocrine, central nervous system and brain effects, skin toxicity and compromises the immune system
- Ecamsule - carcinogenic
- Homosalate - endocrine disruption
- Methylparaben - interferes with genes
- Octocrylene - found to be persistent and bioaccumulative in wildlife, liver issues and carcinogenic
- Octyl Methoxycinnamate - accumulates in the body, disrupts liver and is a carcinogen
- Octyl Salicylate - broad systemic effects in animals at moderate doses
- Oxybenzone - carcinogen and contributor to vascular disease, may affect the brain and nervous system in animals
- Padimate O - carcinogen
- Phenylbenzimidazole - carcinogen
- Phenoxyethanol - irritant, carcinogen, endocrine disruption
- Sulisobenzone - strong evidence of skin toxicity, affects sense organs in animals
- Titanium Dioxide - carcinogen when in nanomaterial form
- Zinc Oxide - bioaccumulative in wildlife, evidence of reproductive toxicity
Sunscreen Information: E.W.G. 6/1/2011 - Sunscreen And Skin Cancer
Sunscreen Information: Natural News 8/2/2011 - Astaxanthin Naturally Prevents Sunburn
Sunscreen Information: Dr. Mercola 10/15/2000 - Sun-Care Chemical Proves Toxic In Lab Tests
Sunscreen Information: Dr. Mercola 6/19/2000 - Sunscreen Products Actually Promote Cancer
Sunscreen Information: Dr. Mercola 9/25/2007 - Hidden Danger In Sunscreens