Your Guide to Sunscreen
by Isabella Portocarrero
Reviewed by Dr. Peter Bittar
Why Do We Need Sunscreen?
Ultraviolet (UV) rays from the sun can be extremely harmful. They can cause sunburns, accelerate skin aging (such as wrinkles and sunspots), and increase the risk of skin cancers. Sunscreen is one of the most important tools for protecting our skin from these harmful effects. While everyone benefits from daily sunscreen use, choosing the right one can be confusing. Here is what you need to know.
Mineral vs. Chemical Sunscreen
Mineral (Physical) Sunscreens:
Mineral sunscreens use active ingredients like zinc oxide or titanium dioxide to protect the skin. Upon application, mineral sunscreens immediately offer protection by reflecting and scattering UV rays. In contrast to chemical sunscreens, mineral sunscreens are less likely to cause irritation, making them ideal for sensitive skin or eczema. However, mineral sunscreens tend to leave a white cast on the skin if they are not tinted. For this reason, a tinted mineral sunscreen is often recommended for a more natural appearance and better blend across all skin tones.
Chemical Sunscreens:
Chemical sunscreens use active ingredients such as avobenzone, oxybenzone, octinoxate, and octocrylene. Upon application, chemical sunscreens require 15–20 minutes to fully absorb into the skin and form a protective layer. They provide protection by absorbing UV radiation and converting it into harmless heat, which is then released from the skin. Unlike mineral sunscreens, chemical sunscreens are often easier to blend into the skin and typically do not leave a white cast.
Understanding the Ingredients
The active ingredients in sunscreen determine how it protects you:
● Mineral Filters: Zinc oxide and titanium dioxide provide full broad-spectrum protection on their own by reflecting and scattering UV rays.
● Chemical Filters: Combine ingredients to cover UVA and UVB. For example:
○ UVB filters: octinoxate, homosalate, octocrylene, octisalate
○ UVA filters: avobenzone, oxybenzone
● Iron Oxides: Often found in tinted sunscreens, they protect against visible light, which is especially helpful for preventing hyperpigmentation in darker skin tones and for preventing flares of melasma, which be sensitive to visible light as well.
Broad Spectrum vs. SPF
When choosing a sunscreen, it's important to understand terms like SPF and broad-spectrum.
SPF (Sun Protection Factor): Measures protection against UVB rays, which cause sunburns. The amount of UVB that gets through is calculated by dividing 1 over the SPF: For example, SPF 30 will let in only 1/30th (3%) of UVB. For the best protection, choose a sunscreen with SPF 30 or higher, as it blocks about 97% of UVB rays and provides stronger defense against sunburn and skin damage.
Broad-Spectrum: Means the sunscreen protects against both UVA and UVB rays, which is essential since UVA rays penetrate deeper into the skin, contributing to aging and increasing cancer risk.
To learn more about the differences between UVA and UVB rays, read our article “UV Radiation: How Sun Exposure Ages and Harms Your Skin”.
Water Resistance
When choosing a sunscreen, water and sweat resistance is key. The term water- or sweat-resistant means that the SPF is maintained after 40 to 80 minutes of activity in water or sweating.
Common Myths
Time of day does not matter.
UVA rays are strongest from 10 a.m. to 4 p.m., but skin damage can still occur anytime the sun is up through UVB rays.
Clouds, rain, or winter mean no sunburn.
Up to 90% of UV rays pass through clouds. Snow, water, and sand reflect UV, increasing exposure. We recommend you use sunscreen year-round, regardless of weather.
Dark skin doesn’t need sunscreen.
Higher melanin levels in darker skin provides protection of up to 13 SPF at most. While it offers some natural protection, UV rays can still cause skin damage, including wrinkles and cancer. Everyone needs sunscreen, regardless of skin tone.
My makeup has SPF—that's enough.
Makeup with SPF provides limited protection and often isn’t applied evenly or on all exposed areas. Use sunscreen underneath and apply it to all sun-exposed skin.
Higher SPF gives much better protection.
SPF 30 blocks 97% of UVB and SPF 100 blocks about 99%. No sunscreen blocks 100%. All sunscreens last about 2 hours, so reapply often, especially after water or sweat.
References
Baron ED. Selection of Sunscreen and Sun-Protective Measures. In: Elmets CA, Corona R, eds. UpToDate. Updated October 31, 2023. Accessed June 18, 2025. https://www.uptodate.com/contents/selection-of-sunscreen-and-sun-protective-measures
Dixon M. Myth or fact: Coconut is an effective sunscreen. Mayo Clinic Health System – Speaking of Health. Published July 22, 2013. Accessed June 18, 2025. https://www.mayoclinichealthsystem.org/hometown-health/speaking‑of‑health/myth‑or‑fact‑coconut‑is‑an‑effective‑sunscreen
UpToDate. Photoaging. Updated February 23, 2024. Accessed July 10, 2025.https://www.uptodate.com/contents/photoaging
UpToDate. Selection of sunscreen and sun-protective measures. Updated October 31, 2023. Accessed July 10, 2025. https://www.uptodate.com/contents/selection-of-sunscreen-and-sun-protective-measures