UV rays from the sun cause somewhere around 90% of the visible signs of aging. For this reason, I am a little bit fanatical about sunscreen (as you should be to) and in preparation of summer (starts officially June 21st!) I am organizing and sharing all the information I have read, made note of, and compiled about sunscreen over the past couple of months.
There is a lot of information I want to share so I have organized it as following and am calling this whole thing the Sunscreen 101 Series:
In Pt 1 (that’s this post!) :
What are UV rays? The difference between UVA and UVB rays
How do Antioxidants Play a Role in Sun Protection?
Part 2 :
All about UV Filters, Chemical & Physical, FDA-Approved and Non-Approved
So let’s get started!
There are three classifications of UV rays, UVA, UVB, UVC. Each classification represents a range of wavelengths. As the letters go up, the wavelength of the rays becomes shorter and the intensity of the rays become stronger. Here is an illustration:
UVC rays have the shortest wavelengths and the most energy. Luckily, most UVC rays are filtered out by the stratosphere and whatever does manage to make its way through gets filtered by the ozone layer. For all intents and purposes, you don’t need to worry about UVC rays unless you’re climbing Mt. Everest in which case you honestly have bigger issues to worry about.
UVB have more energy than UVA rays but less than UVC rays. Even though UVB are less prevalent than UVA on Earth’s surface, they are more intense and are the chief cause of redness and sunburn.
Although not as intense as UVB, UVA are more prevalent, with some sources saying they make up 95% of solar radiation that reaches the Earth’s surface, penetrate the skin more deeply, and are not affected by cloud cover or windows. UVA rays are responsible for photoaging (skin aging and wrinkles ). Both UVA and UVB cause tanning.
Here is a graph summarizing some key differences between UVA and UVB rays.
UVA UVB Primary cause of sunburn and reddening Not affected by change in season, altitude, or weather Strongest in summer months and at high altitudes. Also, 80% of UVB rays will bounce off of reflective surfaces like snow or ice. Penetrates clouds and windows May be filtered by clouds. Does not penetrate glass Does not induce melanogenesis but can oxidize / polymerize existing melanin to be darker Induces melanogenesis (tanning) Less carcinogenic than UVB but studies show UVA rays cause damage to skin cells called keratinocytes in the basal layer of the epidermis where most skin cancers occur Key role in development of skin cancer – UVB rays result in direct photochemical damage to DNA from which gene mutations arise Primary cause of visible signs of aging Contributes to photoaging
The take-away is you need to protect yourself against both. No surprise there.
UVA protection is severely underrated by both the consumer marketplace and regulatory agencies. SPF, for instance, is a measure of UVB protection, which means that godawful SPF 100 stuff you’re smearing on yourself at the beach will prevent sunburn but leaves you vulnerable to tanning, skin cancer, and photoaging. as of 2012, the FDA changed its regulations such that sunscreens labelled “Broad Spectrum” are required to pass a test showing it provides UVA protection proportional to its UVB protection. This is a huge step in the right direction, but one of the biggest problems with the FDA is that there are so many UVA filters that are excellent and stable (unlike avobenzone, the most common UVA filter in the states) approved in Europe and Asia that for whatever reason the FDA hasn’t gotten around to approving.
In the US, there is currently no required UVA protection rating. In other countries, there are a few methods by which UVA protection is measured:
- PPD – Persistent Pigment Darkening
- UVA exposure is reduced by a factor of the PPD rating
- i.e. a PPD of 10 indicates a person is exposed to 1/10th as much UVA as she would be without protection
- European sunscreens usually use the PPD rating system
- PA – Protection Grade of UVA
- Corresponds to PPD rating as follows:
- PA+ ⇒ PPD 2 – 4
- PA++ ⇒ PPD 4 – 8
- PA+++ ⇒ PPD 8 – 16
- PA++++ ⇒ PPD 16+
- Asian sunscreens usually use the PA rating system
- Corresponds to PPD rating as follows:
- UVA Seal
- Indicates the proportion of UVA protection to SPF protection is at least ⅓
- This seal is used in the EU
If you’re in the US where quantifying UVA protection is not required and feel uneasy about trusting broad spectrum classifications, the best way to make sure you are protecting yourself from UVA rays is to check the sunscreen for UVA filters! Post about all the sunscreen filters out there is coming soon, but in the meantime, what you want to know is to look for the following ingredients: Zinc Oxide, Avobenzone, Tinosorb S, Tinosorb M, Mexoryl SX, Mexoryl XL, Helioplex, Uvasorb HEB, Uvinul A plus, Bisdisulizole Disodium, and Meradimate.
UVA protection doesn’t end with filters though! Antioxidants can play a significant role in UVA (and UVB) protection, but more on that later.
UVB is all about SPF protection, which is hopefully a somewhat familiar topic. There is a lot of potentially conflicting information about SFP and hopefully I will be able to help bring some clarity.
SPF is measured similar to how PPD is measure (or more accurate, PPD is measured how SPF is measured). UVB damage is reduced by a factor that is the SPF rating. The effectiveness of sunscreen is measured by multiplying the SPF factor by the length of time it takes for an individual to suffer a burn without sunscreen. In general, this means a sunscreen with SPF 15 will filter out all but 1/15th of the UVB radiation hitting your skin. You may have heard that higher SPFs have diminishing sun protection capabilities, and this is true. If you do the math, you will find that SPF 15 offers 93.3% protection from UVB rays. When the SPF is doubled (SPF 30), the percent protection only goes up 3.3% to 96.7% protection. Doubling it further (to SPF 60) offers a even less impressive return, providing 98.3% protection. A graph of the diminishing returns of higher SPFs is graphed below:
Don’t go throw out all your SPF 50 sunscreens yet! As with all things sun, UV, and sunscreen related, this issue is a lot more complicated than the graph above indicates. Consider, for instance, the following physical sunscreens:
- Naked Turtle Sunscreen SPF 30 with 10% Titanium Dioxide and 5% Zinc Oxide
- Coola Mineral Face SPF 30 Sunscreen Lotion with 6.3% Titanium Dioxide and 3.5% Zinc Oxide
Both of the sunscreens above have an SPF of 30. However, the Naked Turtle sunscreen contains 59% more titanium dioxide and 43% more zinc oxide than the Coola sunscreen. I point this out to illustrate that there is more to determining the SPF (and PPD) rating of sun-protection products than the concentration of active ingredients. In fact, SPF ratings are determined by a test standardized by the FDA. This is important for a few reasons:
- Do not DIY sunscreens or buy unregulated sunscreens (i.e. off Etsy)
- Apply generously and liberally
When the SPF of sunscreen is tested, per FDA protocol 2.0mg/cm2 of sunscreen applied to a plate, a device used to measure the efficacy of sunscreen. This means the SPF advertised on a bottle of sunscreen assumes the surface area of your skin is covered by 2.0mg of product per square cm. If you extrapolate that quantity to an average sized face, it equates to about ¼ of a teaspoon of sunscreen for just your face.
If you apply less than 2.0mg per square centimeter of skin, you will not achieve the sun protection factor specified for the product. Per the Skin Cancer Foundation, most people only apply somewhere between .5mg to 1mg of product per square centimeter of skin, and consequently only achieve approximately ⅓ of the labelled SPF value. That means most people are only getting SPF 10 out of their SPF 30 sunscreens. Using a high SPF sunscreen allows for a margin of error in the application volume.
Lastly, robust UVB filters are easier to come by in the US than UVA filters. Look for Zinc Oxide, itanium Dioxide, Tinosorb S, Tinosorb M, Helioplex, Octinoxate, Octisalate, Homosalate, Uvinul T 150, Ensulizole, Dioxybenzone, Trolamine Salicylate, Uvasorb HEB, Parsol SLX, and Amiloxate.
How Antioxidants Play a Role
Anyone who has spent half a second shopping for skincare know that antioxidants is a major buzzword. To review:
An antioxidant is a molecule that inhibits the oxidation of other molecules. Oxidation is a chemical reaction involving the loss of electrons or an increase in oxidation state. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When the chain reaction occurs in a cell, it can cause damage or death to the cell. Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions. They do this by being oxidized themselves, so antioxidants are often reducing agents such as thiols, ascorbic acid (vitamin C), or polyphenols.
In short, antioxidants are an extra line of defense against all sorts of damage that may otherwise affect your skin. UV rays are responsible for a lot of damage (again, 90% of the physical signs of aging are due to UV rays). How to antioxidants play a part? Well, consider the following offered by a comparable study of the photocarcinogenesis of UVA and UVB rays:
UVA radiation is hardly absorbed by DNA. Hence, the absorption by other molecules (endogenous photosensitizers) becomes more important, thus radicals and, more specifically, reactive oxygen species can be generated that can damage DNA, membranes, and other cellular constituents.
The reason this passage struck my eye is because I’ve heard many times before that Vitamin C and E are photo-protective, and this seems to point to an explanation for why. Per wikipedia:
The conclusion this all seems to lead to* is that with UVA ray exposure, there seems to be an opportunity to stave off UVA damage not only by utilizing UVA filters but also utilizing antioxidants to interfere with the oxidative damage initiated by exposure to UVA rays.
At this point, I consulted a biologist friend of mine who does cancer research and is a lot more qualified to interpret and understand pubmed articles than I am. His input? Reactive oxygen species are either oxidizing agents or free radical initiators. In theory, antioxidants react with reactive oxygen species to prevent it from forming radicals in the body. In addition, he heavily stressed this interaction works in theory and has only been verified in in vitro (in a test tube or on a petri dish), but in vivo (i.e. in actual living, breathing bodies), the mechanisms for that relationship are not well studied or verified. He also cautioned to always take in vitro findings with a bucket of salt, because they don’t usually have meaningful implications. In vivo studies are expensive so oftentimes to get funding / approval, an in vitro study is done first. If a relationship cannot be established in an in vitro study, there is usually no point in carrying out an in vivo study. If the in vitro study does demonstrate a relationship, it may or may not (and usually does not) produce the same results in vivo. I may be paraphrasing / over simplifying this conversation a bit, but he did offer, as a clarifying example, that anyone can cure cancer in vitro.
Getting back on topic, he did feel good about one particular in vivo study (done on pigs) which is the quite well known and frequently cited, done by a Duke professor turned Skinceuticals founder Dr. Sheldon Pinnell, which found that Vit C enhances UVA protection and that the combination of 0.5% ferulic acid, 15% L-ascorbic acid, and 1% α-tocopherol increases the stability of the antioxidants and doubles photoprotection.
This study is key, because that specific combination of 0.5% ferulic acid, 15% L-ascorbic acid, and 1% α-tocopherol has become the gold standard of vitamin c serum formulations. There is also another study collaborating the efficacy of Pinnell’s combination, demonstrating that on female mice, topical CE Ferulic prevents the development of malignant skin tumors on skin exposed to UVB rays. It is worth mentioning that the same study compared this CE Ferulic combination with pure Vitamin E, and pure Vitamin E actually increased tumor growth rate. The take away here? Antioxidants have potential to stave off sun damage. They also seem to have the potential to increase sun damage. Do your research before bombarding your skin with every antioxidant under the sun (har har) or stick to known combinations (i.e. CE Ferulic) when in doubt.
Another complication that antioxidants pose is that any protection provided by antioxidants is included in the SPF measure. Recall that the effectiveness of sunscreen is measured by multiplying the SPF factor by the length of time it takes for an individual to suffer a burn without sunscreen. Let’s say you have a hypothetical topical cream containing 5% of sunscreen filter X has an SPF of 15. Let’s also say, that by adding a specific combination on antioxidants to this cream, UV damage is reduced by a factor of 2. Because UV damage is reduced by a factor of two, it takes twice as long for you to develop sunburn, so your net SPF effectively increases to 30. However, your UV filters has not increased, so your skin, with the sunscreen + antioxidant cream, is being exposed to the same amount of UVB rays as it would with the sunscreen-without-antioxidants cream, even though the theoretical SPF for the sunscreen + antioxidants is higher.
Lastly, I found an excerpt in a book on Photodermatology about antioxidants used for photoprotection. Here are a few bulletpoints:
- [I]n healthy individuals, six months of daily oral supplementation of 400 IU of vitamin E did not result in any photoprotection to UV-induced skin damage
- Another antioxidant, beta-carotene (120 – 180 mg/day), is known to diminish the photosensitivity in erythropoietic protoporphyria
- In mice, topical tocopherol (vitamin E) or topical L-ascorbic acid (vitamin C) could suppress the induction of UV-induced inflammation, prevent photoimmunosuppression, and decrease UV-induced photocarcinogenesis
- Topical application of green tea extracts have been reported to decrease inflammation, carcinogenesis, and immunosuppression. It has been estimated that the above effect can be achieved with 10 caps of green tea a day, a relatively large amount of ingestion
Summary of Part 1
The TL;DR is this:
- Apply your sunscreen generously and wear it year round
- Don’t forget to check for UVA filters
- Antioxidants may help stave off negative effects of UVA exposure, so add some Vit C with Vit E and Ferulic Acid to your skin routine and some carrots and green tea to your diet
See Part 2 Here.