Happy Labor Day Weekend! I hope you will be spending the long weekend doing something fun in the great outdoors. Since I worked for a top sunscreen manufacturer and live by the ocean, I always show up to the beach with a variety of products to share. This often leads to questions on the differences between the products and their ingredients. Today, I'd like to share some basic information about sun protection and how to make an informed decision when you buy a product.
The first thing you likely notice on a product's package is the SPF level. SPF stands for "sun protection factor" and is an indication of how long you can spend in the sun without getting a sunburn. To calculate this number, clinical testing is performed on the product. The formula is applied to test subjects with a variety of skin types and the time it takes for redness to appear is measured. The rule of thumb is that the SPF value is a multiplier of the time you can spend in the sun without getting burnt. If you could normally last 10 minutes without a burn, SPF 30 will protect you for 300 minutes or five hours. In reality, if you are sweating and getting in and out of a pool, the duration of protection will be shorter than five hours and more frequent reapplication is needed.
There is some debate over the effectiveness of higher SPF values because of this practical dimension. To be fair to manufacturers and brands, a product with an SPF level of 70 or 100 includes a high concentration of active ingredients and meets that SPF level in the controlled setting of the clinical laboratory. However, since regular reapplication is needed in reality, there may be limited benefit to paying more for the highest SPF products unless you are extremely fair skinned and burn easily. Dermatologists recommend an SPF of at least 30.
To go a bit deeper into the science, you may remember from high school science class that the light spectrum we can see as humans is called the "visible spectrum" and ranges from violet to red with wavelengths of 400 to 700 nanometers. Ultraviolet (UV) light has shorter wavelengths that we cannot see. Within the UV spectrum, there are two types of rays that can damage the skin and lead to cancer known as UVA (315 - 400 nm) and UVB (280 - 315 nm). The SPF level indicates the protection from UVB rays as these cause sunburn. However, UVA rays also cause skin damage and penetrate deeper into the skin. In some countries, the ratio of protection for UVB and UVA rays is regulated, but this is not the case in the United States. In order to protect your skin against both UVA and UVB rays, you should look for the claim "broad spectrum" on the package.
Chemical vs. Physical Active Ingredients
If you read my post on regulatory basics found here, you may remember the drug facts box found on all over-the-counter (OTC) products. For a quick refresher, sunscreens are considered OTC monograph drugs by the FDA and therefore include a drug facts box on the packaging. This box includes the list of sunscreen active ingredients and the concentration in the formula for each ingredient. The most common distinction between sunscreen active ingredients is chemical vs. physical as these two types protect the skin by different mechanisms.
The most common chemical sunscreens approved in the FDA monograph include avobenzone, oxybenzone, octisalate, octocrylene, homosalate, and octinoxate. Chemical sunscreens are absorbed into the skin and work by absorbing UV rays and converting that energy into heat. These ingredients offer protection against different wavelengths of light and are therefore typically combined in sunscreen products in order to provide broad spectrum coverage.
The two approved physical sunscreens are zinc oxide and titanium dioxide. Products containing these ingredients may also be called sunblock because they literally block the UV rays by forming a barrier on the skin that reflects the UV wavelengths. Since these ingredients provide a physical barrier on the surface of the skin, they typically have a whitening effect and may bring back memories of white-nosed lifeguards.
In July 2018, legislation passed in Hawaii banning sunscreens containing the ingredients oxybenzone and octinoxate due to the potential for damage to coral reefs. As a result, there has been a recent industry trend of products labeled as "reef friendly". There is not a clear definition of what is meant by the term. It could simply mean the product does not contain the banned ingredients, or it could mean that product does not use any chemical sunscreens and contains zinc oxide or titanium dioxide.
Another recent debate topic has been the usage of physical sunscreens with nano-sized particles (between 1 and 100 nm). Smaller particles are desired by formulators because they reduce the whitening effect on the skin. The current research indicates that zinc oxide and titanium dioxide particles do not penetrate the skin, either in nano or non-nano forms, and are therefore safe to be used in cosmetic products with one exception. The European Union banned the usage of nano particles in spray products due to the potential safety concerns of inhalation. There is additional research needed on the impact of nano particles on the environment.
When deciding which product to purchase, there are additional considerations about what may work best for your skin. Physical sunscreens tend to be a better fit if you have sensitive skin, but they can be difficult to rub in if there's a high concentration of the active ingredient. Chemical sunscreens work well if you are sweating or swimming since they are absorbed into the skin and are not a physical barrier that can be washed away.
For me personally, I tend to use physical sunscreen on my face and chemical sunscreen on my body. The skin on my face is more sensitive and tends to be irritated by chemical sunscreen ingredients, especially around my eyes. I use a BB cream with a tint that eliminates the concerns about whitening. For my body, I prefer a product that is easy to rub in so I am confident that I have full coverage. I tend to gravitate to products that absorb into the skin like a normal moisturizer and don't have an oily or sticky feel.
As with any skincare choice, I recommend trying a variety of products to see what works well for you since everyone's skin and preferences are unique. Do you have any favorite products? Any additional questions on sunscreens or other product types you would like me to explain in the future? Please let me know in the comments below!