Sunscreens and Skin Damage from Sun Exposure

From Beachapedia

Sunscreen Basics
Sunscreen is used to protect skin from the damaging effects of the sun. Effective sunscreens protect against both UVA and UVB radiation, as both UV types reach the Earth’s surface and can cause negative effects to human skin and health. UVB is most affiliated with redness from sun exposure and squamous cell carcinoma (epidermis issues), while UVA is most affiliated with loss of skin elasticity and collagen damage , as well as skin cancers like melanoma (dermis issues).[1]

“Sunscreens are used to protect the skin against the harmful effects of solar ultraviolet (UV) radiation. Part of this radiation, UVC (100–290 nm), is filtered off from the atmosphere mainly because wavelengths smaller than 242 nm are absorbed by stratospheric molecular oxygen to produce ozone. This stratospheric ozone can partly absorb UVB (290–320 nm) rays. But most of the remaining UVB together with UVA (UVA-2, 320–340 nm; and UVA-1, 340–400 nm) rays reach our skin and cause biological and metabolic reactions.” - Excerpt from Smijs & Pavel, 2011.

To backtrack, our skin has two main layers, the outer layer called the epidermis, and the inner layer called the dermis. The outer part of the epidermis is the stratum cornum (or SC). The SC is vital in blocking chemicals and materials in the outside environment from absorbing into the body: however, the skin can still be permeable due to impairments (psoriasis), and appendages (hair follicles and sweat glands), in addition to other cellular pathways. UVB exposure can also make this outer epidermis layer more permeable to outside substances.[2]

Diagram of Skin Layers

Figure 1. “The viable epidermis, underlying the SC, contains three layers, the stratum basale, the stratum spinosum, and the stratum granulosum. The SC consists of approximately 15 layers of corneocytes. The main cell type in the viable epidermis is the keratinocyte. Pathways for cutaneous penetration include the paracellular (a), transcellular (b), and the transappendagael route, which includes the transport along hair follicles (c1), sweat pores (c2), and sebaceous glands (c3)” – Excerpt and image from Smijs & Pavel 2011."

What's the Difference and Value of “SPF”
SPF stands for “sun protection factor” and is quantified based on the ability of sunscreen to protect against UVA and UVB radiation (but mainly UVB). Many believe that higher SPFs, like 80 or 100, are significantly more protective than lower SPFs. In reality- this is not the case. Proper application of 2 milligrams sunscreen per square centimeter of skin with SPF 30 sunscreen blocks 97% of UVB rays, while SPF 50 blocks 98% of UVB rays. And the increases in protection get even less dramatic the higher up in SPF you go.[3]

Several doctors recommend that people use an SPF no less than 30, and no more than 50. It’s also recommended to reapply frequently and still avoid direct sun exposure as much as possible. Note – if your sunscreen doesn’t say “broad spectrum”, it means that sunscreen only protects against UVB radiation, not the extremely harmful UVA radiation! Learn more from the Skin Cancer Foundation and the Environmental Working Group (EWG).

Make sure your sunscreen has ingredients that also protect against UVA radiation – including zinc, titanium dioxide, avobenzone, or oxybenzone, to get full coverage. However, if you’re going into the ocean, river, or lakes – please be careful to avoid any products containing oxybenzone and be mindful of ingredients listed on the HEL list, as they have been found to cause damage to coral reefs and harm marine wildlife. We are working on a new article about “reef friendly sunscreens” but in the meantime, learn more about reef friendly sunscreens from Dr. Craig Down's Haereticus Environmental Laboratory and from the Alert Diver.


  1. Smijs, TS. & Pavel, S. 2011. "Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness". Nanotechnical Science Appplications, 4:95-112.
  2. Smijs, TS. & Pavel, S. 2011. "Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness". Nanotechnical Science Appplications, 4:95-112.
  3. Wang, S.Q. 2010. "Does a higher-SPF always protect your skin better?". Skin Cancer Foundation.