Why Applying Sunscreen First Provides the Best Protection from the Sun
The subject of what order in your skincare regimen you should apply sunscreen has fortunately generated stimulating discussions on DermTV and in other forums, and has gotten many people thinking about this important subject. One of the reasons there is so much discussion is that it's a very complex topic without a short answer. My education, over thirty years as a practicing dermatologist, and countless hours of medical reading have led me to strongly believe (as do most of my medical peers) that as a rule of thumb, in order to get the most effective protection from your sunscreen, you should apply it first. While there are almost always exceptions to any rule, just as the topic as a whole isn't simple, an exception to this rule isn't as easy as stating that, "if sunscreen is put on the surface of the skin, and exfoliants destroy skin surface cells, then exfoliants applied on top of sunscreen destroy sunscreen," which was an actual statement made by a consumer on the topic recently. In fact, logical but simplistic reasoning can even lead one astray since the science of this subject, as you will see, can result in counter intuitive facts and conclusions, and is further distorted by many variables. To frame this discussion, I am going to first talk about why you should apply your sunscreen first, then discuss it in context of an example second product (an exfoliating product), and finally bring in all of the confusing variables. As you will see below, I am presenting this discussion in a bullet point fashion, and if you have previously been following this topic in the comments section of DermTV episodes (e.g., Does Makeup with SPF Really Protect from the Sun), you can skip the "A Simple Explanation" section which rehashes what was said during those discussions but is very important for anyone reading about this topic for the first time.
Please note that in order to tackle this complex subject as clearly as possible, since chemical sunscreens (e.g., organic, carbon based, traditional) and physical sunscreens (e.g., Zinc and/or Titanium based, physical) work differently, I will separate my discussion into two different articles. In this article, I will focus only on chemical sunscreens, and thus anywhere that I refer to sunscreen I am referring to chemical sunscreen. In the coming days/weeks, I will discuss chemical free sunscreens in a separate article.
A Simple Explanation (But Don't Stop Here)
- In order for you to get the best chance of receiving the stated SPF and sun protection from a sunscreen, it should be applied first, before any other skincare products (e.g., exfoliators, moisturizers).
- The SPF that you see on sunscreen bottles is strictly measured and signed off on by the Federal Drug Administration (FDA) in tests that require that sunscreen is the only product/ointment/solution that is on your skin. However, as Joshua Powell (also known as "Skincareman" on Internet message boards) stated in one of his comments on DermTV, this doesn't prove that putting other products on first will interfere with the sunscreen (or even that putting products on top of sunscreen wouldn't interfere either). And Josh is absolutely correct. In the best of all possible worlds, I would suggest that people wear only sunscreen to protect themselves from the sun. But of course I have to be realistic and understand that people will use several products. However, since skin cancer is the most prevalent form of cancer in the United States, I would prefer to (and recommend that my patients do as well) simulate testing situations to the best of my (their) abilities which would lead one to put sunscreen on first.
- Chemical sunscreens work by absorbing ultraviolet (UV) rays. In order to accomplish this, it must first be absorbed onto and into the skin, and activate (hence why sunscreen directions state to apply it twenty to thirty minutes prior to sun exposure). On the basis of the above, prior to applying sunscreen, I wouldn't want to have any other products on and or absorbed into my skin because of their potential to interfere with this absorption or activation process of sunscreen (and thus limit or eliminate the efficacy of it). Thus, this is another reason that I always recommend to apply sunscreen first.
- Whether chemical or physical, I always recommend an even application of sunscreen across your skin to ensure optimal protection. If you apply other products first (e.g., foundation with spf or even a moisturizer), you can't know whether or not you're getting an even application. Personally, I'd prefer to have an even application of sunscreen that protects me from skin cancer and risk small patches of dry skin resulting from my moisturizer not being applied evenly, than vice versa.
Adding an Exfoliating Product Into the Mix
- At home, consumer-friendly chemical exfoliants work by a process of evolution (i.e., very slowly), gradually dissolving the most superficial few layers of dead cells on the very top of the skin (stratum corneum). And the purpose of exfoliation (whether for facial rejuvenation or the treatment and prevention of acne) requires that the exfoliants work only very superficially. It is because it is such a superficial and gradual process that it needs to be (or should be ) repeated every other day, or even daily, depending on the strength of the exfoliant.
- As already discussed, sunscreen takes approximately twenty to thirty minutes to become activated and effective at absorbing UV rays (i.e., protecting you from sun damage). During this period, the sunscreen's molecules bind to the surface of your skin, and in addition, a meaningful amount of the sunscreen's molecules also penetrate below the surface into the epidermis, and then even lower, into the dermis. Since the dermis is where blood vessels are, as the sunscreen's molecules reach the dermis, they also reach the bloodstream and then are disseminated throughout the body. This deep penetration of sunscreen was proved by researchers finding measurable quantities of sunscreen molecules and metabolites in the urine samples of test subjects who applied sunscreen. For the molecules to have ended up in the urine, they must have entered and then traveled through the blood stream to the kidneys. To reach the blood stream, the molecules must have first enter and travel through the epidermis and then at least half of the dermis. And if measurable amounts were detected in the urine, then we can also conclude that additional unmeasurable sunscreen must also have been absorbed into the different layers of the skin as it traveled from the epidermis to the dermis and then into and through the bloodstream to the kidneys.
- If at home, consumer-friendly exfoliating products went beyond the superficial layers of the stratum corneum and also peeled the lower layers of the epidermis and/or then the dermis (the levels to which sunscreen is absorbed into the skin), you would have large, oozing holes in your skin. Since this doesn't occur when you use at home exfoliating products (or at least I sincerely hope not!), at-home exfoliating products have no access to, or effect on, a large reservoir of the sunscreen that has been absorbed into your skin that helps to protect it.
- Particular to exfoliating products, to further substantiate my belief that exfoliants do not meaningfully deactivate sunscreen, some sunscreens even have glycolic acid combined into them (e.g., DCL-brand Skin Renewal Complex, an SPF 20 chemical sunscreen containing 10% glycolic acid). In order for the sunscreen to receive it's SPF rating (20 in this case), it must demonstrate that SPF in a standardized FDA test by an independent FDA-approved laboratory, which it did. That demonstration of the stability of the SPF of the sunscreen combined with glycolic acid also substantiates how non-aggressive even combined 10% glycolic acid is in not compromising the SPF nor impairing sunscreen molecules.
Adding the Variable of Vehicles (and Exceptions)
As a general rule with chemical sunscreens, I have maintained in previous online discussions as well as in multiple episodes of DermTV that sunscreen should go on first. Since I aim to keep DermTV videos to three minutes or less, I opted to provide a rule of thumb instead of discussing every exception, but this article is clearly the appropriate place to discuss variables and exceptions. And the exceptions begin to arise when we discuss "vehicles." (I will continue to use an exfoliating product as the example product in this discussion.)
- All skin care preparations (e.g., sunscreens, exfoliants, moisturizers, antioxidants, acne medicines, etc.) have two phases: the first is the active ingredient that does the work and the second is the vehicle which carries the active ingredient (e.g., a cream, ointment, lotion, solution, etc.). The active ingredient is dissolved or suspended in the vehicle.
- The active ingredient is usually a single, often small molecule usually comprising far less than one-percent of the skincare preparation's volume and weight.
- The vehicle usually consists of greater than 99% of the skincare preparation's volume and weight.
- If the vehicle of a skincare product (Product A) is more volatile, thinner or evaporates faster than the vehicle of a second product (Product B), then Product A should go on first because after its vehicle (e.g., alcohol or water) evaporates, it leaves a less than 1% volume of the active ingredient molecules which are easily penetrated by the mass effect of Product B's active ingredient whose vehicle is thicker, less volatile or more viscous. In other words, when multiple skincare products are applied (layered) on top of one another, the products with the most volatile, lightest, least viscous vehicle should be applied first (e.g., water based and alcohol based products, and gels). For example, in my current Stallex product line there is a very effective and popular at home exfoliating product containing 10% glycolic acid in a light alcohol vehicle that is applied from a thin cotton pad. I actually recommend to apply this exfoliator before sunscreen lotions and creams because of the rules of the order of application of vehicles we just discussed. As another example, I also have a lighter (than the glycolic pad) vehicle sunscreen (also applied from a pad) which I would thus recommend to apply before the exfoliating pads.
Ultimately, the decision of when to apply sunscreen is a personal one, but unfortunately consistently repeating the wrong decision can lead to a potentially deadly skin cancer. What I know about this topic is what I've been able to pick up throughout the thirty years of my career as a dermatologist, my studies prior to that, and the conversations I've had with my medical peers (including Perry Robins, M.D., the founder and president of The Skin Cancer Foundation) as well as the medical residents I teach at Mt. Sinai Hospital in New York. While I can't tell you whether or not using sunscreen in combination with other products will diminish its efficacy enough to expose you to damaging UV rays (and I'm not sure that anyone can because this testing isn't required by the FDA), as you can see from the above, I've concluded that to most effectively protect yourself, as a rule of thumb, you should apply your sunscreen first. I will continue to recommend this to my patients (as do my peers and most of my fellow doctors in the medical community). As I also noted, there are exceptions, and I believe that people should abide by these as well (so if that means sunscreen should be applied second because of its and another skincare products' vehicles, then so be it).
I now hope that instead of having to defer to comments such as, "applying sunscreen first isn't logical," you now can make for yourself a more educated decision as to how you believe you can best protect yourself from the sun.
And as I truly believe, you don't have to avoid the sun, you just need to effectively protect yourself when you're in it. For more information about sunscreen and sun damage protection, please visit our episodes about sunscreen and skin cancer.
Neal Schultz, M.D.
PS: As a caveat, if anyone knows of someone whose sunscreen was rendered ineffective as a result of applying their exfoliating products second (or any other product/order combination) I'd greatly appreciate hearing from them so that we can add that to the discussion. To those who don't agree with my suggestion to apply sunscreen first, keep in mind we all have the same goal of trying to make sure that everyone knows in what order to apply their products to most effectively prevent sun damage and stay safe. And any additional information is always helpful.
Bonus: An Intro to Chem-Free Sunscreens (with More to Come Soon)
As mentioned, over the coming days and weeks, I will provide in another article a discussion of the order of application of chem-free sunscreens. However, in the meantime, I wanted to provide to you a simple explanation of why (not taking into account exceptions) I believe that chem-free sunscreen should also be applied first.
Chem free (physical blocker) sunscreens work by literally blocking and reflecting the damaging ultraviolet sun energy off of your skin (unlike chemical sunscreens which work by absorbing and destroying harmful UV rays). So I am the first to admit that they can work to some extent regardless of where in the layering of products they are placed. But, again, if you want them to work predictably and reliably, and deliver the SPF they promise they need to be applied first so that, (1) there is an even and uniform layer on the clean skin, (2) other previously applied products don't dilute the concentration and therefore strength of the sunscreen, and (3) they can deliver the promised SPF (as previously mentioned, when they were tested for their SPF value by the FDA, they were applied alone to the skin). While you will get some protection from chem free sunscreen when applied on top of other products or by reapplying makeup containing them on top of other products or even on top of itself, the protection is not predictable and you may well wind up with areas that are damaged or burned from the sun.