We are all familiar with sunburns and sunscreen. From our first day playing outside, we are taught to put on sunscreen to protect our skin. But why? Why do we need to protect our skin from the sun? And how does sunscreen, if at all, protect us?
What is Skin?
First, we must understand the job and functionality of the skin. The outermost layer of the skin is called the epidermis, and the outermost layer of the epidermis is called the stratum corneum (SC). The SC can be viewed as a brick and mortar structure with corneocytes being bricks and intercellular lipids being the mortar. This acts as the first line of defense against not only tangible threats, but also intangible ones such as ultraviolet (UV) radiation. Although the dermis (layer beneath the epidermis) is much thicker and responsible for skin deformation on a large scale, the SC is responsible for local biomechanical behavior due to its relatively higher stiffness.
How Does the Sun Damage Skin?
Solar UV radiation comes in three types: UVA, UVB, and UVC. The sunlight we see is composed of 90-95% UVA and 5-10% UVB. The epidermis absorbs UVB, which we commonly associate with causing erythema (skin redness) and skin cancer. UV radiation poses a “double threat,” attacking the skin mechanically from two angles. It damages the intercellular lipid in the SC, allowing excess water to leave. This drying stress increases the inherent mechanical stress within the skin, leading to cracking and chapping. Additionally, it decreases the skin’s ability to resist damage by reducing the mechanical stability of the skin. In addition to causing lipid damage, UV radiation decreases cellular cohesion by weakening the protein links holding the corneocytes together.
Can Sunscreen Prevent This?
Regarding biomechanics, sunscreen has two primary components: the carrier and UV filter. The carrier is the base of the sunscreen and the primary vessel for the UV filter. The UV filter does the heavy lifting on the protection side of things and absorbs and/or reflects the UV radiation. Since FDA approval of sunscreen is centered around the ability to prevent erythema, there was a lack of information on how sunscreen actually affected the biomechanical properties of skin. Thus, a study was performed to determine the biomechanical abilities of sunscreen. Cadaver skin was tested in vitro with and without UV radiation and sunscreen. It was found, sunscreen not only greatly reduced the drying stress of skin when exposed to UV, but also when there was no UV. The latter result is likely due to the moisturizing effect of the carrier. The sunscreen was also shown to keep cellular cohesion at a level similar to the control.
Not All Sunscreens are Made Equally
So sunscreen works! It doesn’t just prevent erythema, but also preserves the actual biomechanical properties of the skin itself. Except, does it always? There are multiple types of carriers and UV filters used in sunscreen. A study was done to compare two UV filters with each other. One, OMC, is very commonly used in sunscreen, and the other, DOMBM, is a newer molecule designed to have higher photostability (stability under light). The two UV filters were tested under varying intensities of UVB. While they both performed as expected under the lower UVB intensities, the OMC blend performed significantly worse at the highest UVB intensity. This is because, ironically, OMC degrades when exposed to sunlight. This not only has the adverse effect of reducing its effectiveness, but it also creates byproducts that can further damage the skin. So before you buy your next bottle, do your research and make sure your sunscreen will really protect you.
AI Usage Note: AI was used to summarize articles to assist me in understanding how I could piece them together.