The incidence of skin cancer has been increasing dramatically over the last 40 years. From 1992-2006 non-melanoma skin cancer rates have increased 77%. Melanoma rates in 1977 was about 7/100,000; in 1992 it was about 16/100,000 and in 2006 it was about 20/100,00. The rates of skin cancer are increasing despite the fact that the use of sunscreen has increased during the same time period
Population lives longer (therefore seeing more cancer)
Ozone layer depletion
Medical community and population are better at detecting skin cancers
Sunscreen- although used more frequently- not used in adequate amounts
Sunscreen not as effective as possible.
How does solar radiation cause skin cancers?
Two forms of solar radiation penetrate the earth’s atmosphere. UVB radiation (280-320nm) radiation is short wave length radiation that is associated with sunburn (think UVB like UVBurn). This radiation is stronger in the summer months, does not penetrate water, clouds, or glass; however this radiation does reflect off of water and snow so that in the presence of water and snow doses can be enhanced by 80% as an individual will be exposed to the initial radiation and then a second dose of radiation as it bounces off the water or snow. There is a rather strong association with UVB radiation and non-melanoma skin cancers like basal cell and squamous cell skin cancer. There is also an association with UVB radiation with melanoma. During the late 70’s and early 80’s this form of radiation was felt to be the sole cause of skin cancers and just about every sunscreen product works well in protecting against UVB radiation
The second form of solar radiation that penetrates the atmosphere is UVA radiation. UVA radiation can be broken down into two different wavelengths (UVA2 320-340nm and UVA1 340-400nm). UVA radiation is longer wavelength radiation that is equally as present in the summer as it is in the winter. This type of radiation penetrates glass, clouds, and water, and this type of radiation does not burn the skin but may contribute to tanning. UVA radiation is now known to cause the aging effects of chronic sun exposure like premature wrinkles, sun spots, and rough skin. Recent evidence indicates that UVA radiation is just as much a risk factor for skin cancer as UVB radiation and is likely more associated with melanoma than UVB radiation. A recent study out of Australia indicates a 24% decrease in pre-cancerous lesions with the use of daily sunscreen use as compared to those who use sunscreen only intermittently. Also the only study that shows a reduction in the rates of melanoma with the use of sunscreen compared individuals who wear sunscreen daily to those who wear sunscreen only intermittently. Only the group that used sunscreen daily showed a reduction in the rate of melanoma.
Both forms of radiation penetrate into the skin and damage DNA in the basal layer of the epidermis creating mutations. Rarely, one of these mutations creates an “immortal cell” that then progresses into a skin cancer.
How doe sunscreens work?
There are two types of active ingredients in sunscreen that work a bit differently. Chemical (organic) sunscreens use a combination of chemicals that are mixed and matched to attempt to provide broad spectrum protection from solar radiation. Organic in this sense refers to carbon molecules, not pesticide free. All of these chemicals will absorb solar radiation. The process of absorbing this radiation causes the chemicals in the sunscreen to break down— thus chemical sunscreens, in general, lose effectiveness the longer the sunscreen is exposed to sunlight. Also, many of the chemicals in the sunscreen release free radicals when exposed to sunlight. These free radicals do not do much harm if the chemicals are on the surface of the skin, however some chemicals are absorbed into the skin and so the degradation of the sunscreen occurs in the skin where the DNA of the skin resides and mutations can occur.
Physical (inorganic or mineral based) sunscreens use either titanium or zinc or both to provide sun protection. Zinc and titanium tend to reflect light away from the skin so that the solar radiation never reaches the skin. Some of the zinc and titanium will absorb UV radiation and convert it into heat and infra-red light, but during the process free radicals are created. However, unlike chemical sunscreens, zinc and titanium do not penetrate into the skin so any free radicals created will be on the surface of the skin. The surface of the skin does not contain any DNA so there is no potential for mutations or cancer creation.
How are sunscreens tested?
New guidelines to test sunscreen were mandated into law January 1, 2015. There are three tests done on most sunscreens on the market today.
The first test done is called “Broad spectrum” testing. Sunscreens are tested to make sure that all UVA radiation and UVB radiation is blocked or absorbed by the sunscreen. Radiation from 280-400nm must be blocked by the sunscreen for the sunscreen to advertise that it is “broad spectrum”. This testing is done one time before the sunscreen is exposed to any sort of water or solar radiation. Therefore, a sunscreen can pass the “broad spectrum” testing, but no test is done after water exposure to assure that the sunscreen is still “broad spectrum” after water immersion. Also, recall that solar radiation degrades many of the active ingredients in suncreen, thus a sunscreen may start off as “broad spectrum”, but after 15 minutes, 30 minutes, 1 hour, or 2 hours, may no longer be “broad spectrum” as the active ingredients in the sunscreen are being degraded by the very solar radiation it is blocking.
The second test done is called “SPF” testing. SPF is solely a measure of UVB protection and tells the consumer nothing about UVA protection. The arm of an individual of light complexion is exposed to UVB radiation. The time it takes for the subject to start to show pinkness determines the subject’s baseline untreated time. For the sake of understanding, let us say it takes 10 minutes of radiation exposure before the skin turns pink. Then, the same subject’s other arm will contain the sunscreen and the test is repeated on the treated arm. SPF is a measure of time, and if the treated arm takes 150 minutes to start to turn pink then the SPF of the product is 15 (150min treated time/10 min untreated time=15). SPF is only a measure of UVB protection, and there is no assurance that the ingredients in the sunscreen that are intended to block UVA radiation will behave in the same fashion as the ingredients that block the UVB radiation.
Lastly, “water resistance” testing is done. Basically, water resistance testing repeats the SPF test after either a 40 or 80 minute water challenge. However, unlike real life, the sunscreen is not exposed to solar radiation during the 40 or 80 minutes while the subject is immersed in water. I suppose the best way to explain it would be that water resistance testing would be like applying a sunscreen and then swimming indoors only in fresh water (no chlorine) for 40 or 80 minutes. The test verifies that the sunscreen maintains the SPF level in this situation. Chlorine has been shown, also, to degrade some active ingredients in chemical sunscreens so this test does not simulate the environment in a swimming pool. Due to the fact that many of the active ingredients in chemical sunscreens break down in the presence of solar radiation and chlorine, it is unclear how effective the sunscreen would behave if exposed to both water, chlorine and solar radiation for 40 or 80 minutes which is far more typical of real world situations.
Issues with chemical sunscreens
One of the most popular chemicals in sunscreen is oxybenzone. Oxybenzone is particularly popular because it is an effective UVB blocker and blocks some UVA2 radiation as well and it is absorbed into the skin and then absorbed into the body. Many individuals consider the fact that after Oxybenzone is applied topically it can be found in the urine for up to 5 days after it is applied to the skin, somewhat disturbing, but the vast majority of evidence indicates that the doses of Oxybenzone that end up in the blood stream are negligible and unlikely to cause any sort of systemic effect. That being said, I encourage individuals who are in the sun for prolonged periods of time on a daily basis should avoid oxybenzone as they should be applying and using a lot of sunscreen. Also, the American Academy of Pediatrics suggests avoiding oxybenzone in children under the age of 12.
Oxybenzone is very popular because it is in the skin and therefore will not wash off the skin in water. This ingredient along with octinoxate penetrate the skin and help to obtain large SPF values that can not be washed off as the chemicals are in the skin as opposed to on the skin. That being said, studies show a disturbing issue with Oxybenzone. When oxybenzone is exposed to solar radiation it oxidizes into oxybenzone semiquinone. Oxybenzone in small doses does not appear to have significant detrimental effects, however oxybenzone semiquinone has been shone to react with thiol groups and this, basically, deactivates an enzyme in the skin that is important for free radical degradation. So, there is evidence that the protective effects of oxybenzone’s ability to absorb UVB and UVA2 radiation may well be offset by oxybenzone semiquinone’s tendency to deactivate important enzymes needed for free radical deactivation. Finally, chlorine can react with oxybenzone that renders the ingredient less effective in blocking solar radiation, but also the chlorinated oxybenzone is toxic.
Second, the majority of chemical sunscreens contain avobenzone. Avobenzone is one of the only chemicals that blocks UVA1 radiation. In fact the only 2 compounds that block UVA1 radiation is Avobenzone and zinc. Like oxybenzone, avobenzone breaks down in the presence of solar radiation, but it is often mixed with octocrylene to slow down the degradation process. Unlike oyxbenzone, avobenzone is not absorbed into the skin and sits on the surface of the skin. However, there is not guarantee that avobenzone does not wash off the surface of the skin with water exposure. A sunscreen that uses avobenzone with other chemical UVB blockers to pass the broad spectrum test will still pass the water resistance testing because UVA protection is not checked or verified after water exposure. So, avobenzone can wash off and the sunscreen can still advertise itself as broad spectrum, SPF 50 or whatever and water resistant! So one can be in the sun all day and have absolutely no UVA1 protection after they either get into the water or sweat. This creates uncertainty with chemical sunscreens, as it is not certain whether the UVA protection is still adequate after water exposure.
I am not a big fan of chemical sunscreens not because I feel they do not work or are not effective. What I find concerning is the uncertainty. There may be many conscientious sunscreen manufacturers that combine a number of chemical active ingredients to obtain broad spectrum protection and package it in a vehicle that keeps the active ingredients viable and on the surface of the skin even after water immersion. Unfortunately, there are also sunscreens that take advantage of the fact that some of the chemicals that protect against UVB radiation are absorbed into the skin (and eventually into the body) and do not wash off, but the chemicals that protect against UVA radiation do wash off and there really is no way to know, by reading labels, which chemical sunscreens maintain broad spectrum protection after water immersion and which ones do not!
Zinc oxide, is by far, the most important ingredient in a sunscreen. Zinc is the only active ingredient in a sunscreen that blocks both UVB and all UVA radiation. Thus, if you are wearing a zinc based sunscreen and are not burning, you can also feel safe that you are protected from UVA radiation as well. Zinc oxide is one of the primary ingredients in BanxBlock because of this unique property.
Even though Zinc oxide blocks both UVA and UVB radiation, it is a more effective UVA blocker. Rather large concentrations of zinc are needed to reach an SPF 30 level. Pure zinc sunscreens usually contain over 20% zinc and it is nearly impossible to reach an SPF 40 level with zinc alone. Consequently, we added titanium dioxide to BanxBlock. Titanium dioxide works in a similar fashion to zinc, but is more effective blocking UVB radiation and does not block UVA1 radiation. By using both zinc and titanium we are able to take advantage of the more effective UVB blocking properties of titanium and the more effective UVA blocking properties of zinc to obtain an SPF 40 product and still use less then 20% minerals. The greater the concentration of minerals creates a thicker cream and may also be more comedogenic.
The challenge with a mineral sunscreen is achieving water resistance. This depends upon the inactive ingredients as neither zinc or titanium are absorbed into the skin. We have used primarily natural ingredients like coconut oil, beeswax, shea butter, vitamin C, and green tea extract that will not only help the minerals stick to the skin, but also, many of these ingredients are natural moisturizers and anti-oxidants in their own right. We like to think of Banx Block as a skin care product that is also an excellent sunscreen, and many individuals comment that their skin feels softer after using Banx Block and also Banx Block does not tend to cause acne outbreaks.
If you have ever read the label on a traditional chemical sunscreen it will often warn that the sunscreen should not be used on damaged skin. This includes sun burnt skin, rashes, psoriasis or eczema as damaged skin will absorb the chemicals in sunscreen in far greater concentrations than non damaged skin. BanxBlock is actually great for damaged skin, as it is a natural moisturizer that forms a film over the skin and prevents water loss from the skin and zinc is a known natural antibiotic. Zinc is the primary ingredient in many diaper rash formulations.
Mineral based sunscreen has a number of advantages when compared to chemical sunscreens.
- Zinc containing sunscreens block all UVA and UVB radiation thus if you are not burning you are not getting UVA radiation either. This statement may not be true with chemical sunscreens as ingredients that block UVA may degrade faster or may wash off while the ingredients that block UVB are still present and functional
- Mineral based sunscreens are more photo stable. Once again the SPF rating gives you some idea about the photo stability of the active ingredients that block UVB radiation but tells you nothing about the photo stability of the ingredients that block UVA radiation
- Mineral sunscreens do not react with chlorine.— better for swimming pools
- Mineral sunscreens are not absorbed into the skin or into the body. Even nanoparticles do not tend to absorb into the skin, but that is not settled science as of yet.
Mineral sunscreens have the disadvantage of leaving a whitish color and some preparations are greasy or thick, but all in all we are an ardent believer that mineral based sunscreens are superior to chemical based sunscreens if one is wearing sunscreen to prevent skin cancer.
The topic of sunscreen is complex and there are many other issues that can be discussed. If you have any further questions please feel free to contact me at firstname.lastname@example.org
Jeff Pokorny, MD