There are two types of sunscreens available to protect the skin cells from UV radiation.
- Physical sunscreens (also known as mineral sunscreens)
- Chemical sunscreens
Physical Sunscreens
Physical sunscreens use minerals such as Zinc oxide and Titanium oxide which reflect UV radiation.
They block visible light, UVA and UVB radiation.
Physical sunscreens are less likely to cause skin irritation and allergic reactions and are preferred for individuals with sensitive skin or in babies and children.
Chemical Sunscreens
Chemical sunscreens contain organic (carbon-based) compounds such as oxybenzone, avobenzone, octisalate, octocrylene, homosalate, and octinoxate.
These compounds work by absorbing UV radiation and converting it into heat, which is then released from the skin.
They offer broad spectrum protection, however, some individuals with sensitive skin may experience irritation or allergic reactions to certain chemical sunscreen ingredients
Sunscreen application
To ensure effective sun protection, it is important to choose a sunscreen with an adequate SPF – SPF 15 filters about 94% of UVB rays and SPF 30 filters around 97%, with minimal additional benefit beyond SPF 30.
It’s wise to use sunscreen with an SPF of 30 or higher
One ounce (the amount of sunscreen required to fill a shot glass) has been recommended as a helpful indicator of adequate full body coverage.
Apply sunscreen 20 minutes before sun exposure for it to bind effectively to the skin. Then reapply sunscreen 20 minutes after the initial application, then every 2-3 hours while outdoors
Remember to reapply after swimming, sweating heavily or towel-drying, ever if the sunscreen is water resistant.
Following these guidelines will protect against sunburn, skin cancer, photo ageing and photo pigmentation
Evidence for Sunscreen in the prevention of Skin Cancer
Multiple studies have been performed investigating the efficacy of sunscreen use in the prevention of the development of skin cancer.
Sunscreen use has been demonstrated to decrease the number of existing actinic keratoses, while also decreasing the accumulation of new actinic keratoses.
In a large, 4.5-year, randomized controlled trial performed in Australia, patients randomized to daily use of SPF 16 sunscreen developed significantly fewer squamous cell carcinomas (SCC), but without a significant effect on the development of basal cell carcinomas (BCC). During an 8-year follow-up of those same study participants, SCC development was reduced by nearly 40%. For BCC, the numbers trended downward (a decrease of 25%) during the extended follow-up period, but no statistical significance was seen [1]
A prospective study in Australia demonstrated a decrease in the risk of melanoma and in the proportion of melanomas that were invasive in a cohort that used sunscreen regularly over a period of 5 years with evaluation after a further 10 years [2]. 1621 residents of Nambour were randomised to daily or discretionary sunscreen use over 10 years.
The daily sunscreen cohort had half the number of melanomas (11 vs. 22). There were also less invasive melanomas in the daily sunscreen group. (3 invasive vs. 11 invasive (HR 0.27).
References:
Green A, Williams G, Neale R, Hart V, Leslie D, Parsons P, et al. Daily sunscreen application and beta-carotene supplementation in prevention of basal-cell and squamous-cell carcinomas of the skin: A randomised controlled trial. Lancet. 1999;354(9180):723-9.
Green AC, Williams GM, Logan V, Strutton GM. Reduced melanoma after regular sunscreen use: randomized trial follow-up. J Clin Oncol. 2011 Jan 20;29(3):257–63.