In this episode of Topical Conversations, Dr Ahuva Cices, assistant professor at Icahn School of Medicine at Mount Sinai, introduces why it is crucial for dermatologists and the public to understand the differences between physical and chemical sunscreens and their mechanisms of action (MOA). 

Common misconceptions

Dr Cices addresses a common misconception: that physical sunscreens primarily work by reflecting and scattering UV light. While this was historically true, she clarifies that this is now only a small part of how modern physical sunscreens function.1 Instead, physical sunscreens predominantly absorb UV light, similar to chemical sunscreens. This challenges the outdated understanding that reflection and scatter are the main protective mechanisms of physical sunscreens. 

Modern mechanism of action 

With the advent of micronization and nanoparticle technologies, modern physical sunscreens containing zinc oxide and titanium dioxide have shifted their primary mechanism to UV light absorption.² One study demonstrated that these modern formulations reflect less than 5% of incoming UV light,³ with the majority of protection coming from absorption and subsequent energy dissipation as heat.^2,4 

Implications for dermatologists and patients 

Understanding the MOA of modern physical sunscreens is essential for dermatologists when advising patients. While some dermatologists may prefer physical sunscreens due to their perceived safety and simplicity,¹ it is important to recognize that both physical and chemical sunscreens now work via similar mechanisms. Therefore, factors like cosmetic elegance and ease of use become more significant when recommending sunscreens to patients. 

Dr Cices advocates for dermatologists to stay informed about the current MOA of sunscreens. Dispelling myths and prioritizing user-friendly, cosmetically elegant products can help dermatologists guide their patients in choosing effective sun protection, ultimately enhancing compliance and reducing the risk of sun damage. 

References 

1. Zundell M, Wong M, Rubin C, Cices A, Bitterman A. Improving patient communication on sunscreen choice: Updating mechanistic misconceptions. JEADV Clin Pract. 2023;2:963-964. doi:10.1002/jvc2.251 
2. Smijs T, Pavel S. Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness. Nanotechnol Sci Appl. 2011; 4: 95–112. doi:10.2147/NSA.S19419 
3. Cole C, Shyr T, Ou-Yang H. Metal oxide sunscreens protect skin by absorption, not by reflection or scattering. Photodermatol Photoimmunol Photomed. 2016; 32(1): 5–10. doi:10.1111/phpp.12214