What’s in Your Sunscreen, Part 1: The Most Common UV Filters

As spring approaches and you start stocking up on sunscreen, you're likely to encounter a familiar lineup of ingredients on the back of those bottles. What are they, how do they differ, and which should you pick?

Active vs. Inactive Ingredients

In every sunscreen, you'll see two types of ingredients: active and inactive ingredients. Active ingredients are those that are intended to provide the therapeutic effect claimed by the product, in this scenario protection from UV damage. These are the components responsible for protecting your skin from harmful ultraviolet (UV) radiation. Inactive ingredients, on the other hand, help support the product's function—improving texture, water resistance, shelf life, or cosmetic feel—but they don’t directly shield your skin from UV (at least not enough on their own to be considered active ingredients).

Despite active ingredients being the most important from the standpoint of sun protection, they don't vary much from product to product. Of the best selling sunscreens on Amazon, 95% of them contain the same 6 active UV filters, and usually in nearly the exact same combinations. So, it's likely the reason you are choosing your sunscreen has more to do with inactive ingredients than the active ones. However, there are important distinctions between the active ingredients that should be the foundation upon which you make your selection.

Common UV Filters

There are six active ingredients that dominate the sunscreen aisle. They fall into two broad categories: organic ("chemical") filters and inorganic (mineral or “physical”) filters.

The four additional organic filters  pop up less often but are worth knowing because of their presence in certain popular formulations or concerns about their safety.

Organic vs. Inorganic: What Does It Really Mean?

The terms “organic” and “inorganic” in sunscreen don’t mean what they do in the grocery store. The definition of “organic” here is the chemistry definition: a molecule built around carbon atoms. It does not refer to the agricultural definition which often refers to a food being produced without synthetic pesticides or GMOs.  With respect to sunscreens, these are not naturally occurring molecules.  Organic (carbon-based) compounds, in general, can be natural (like glucose, fatty acids) or synthetic (like avobenzone, plastics).  In contrast, “inorganic” refers to compounds that lack carbon: water (H₂O), salt (NaCl), carbon dioxide (CO₂), and metal oxides like zinc oxide (ZnO) or titanium dioxide (TiO₂). Similar to organic molecules, they can be both naturally occurring or synthetically derived.

How Sunscreens Actually Work

All sunscreens form a film on the skin’s surface that prevents UV radiation from penetrating deeper layers.

Even today it is often believed that organic filters absorb UV light while inorganic filters reflect or scatter it. But research has shown that’s an oversimplification, or even flat out wrong. According to Cole et al. (2016), nearly all UV filters—organic and inorganic—primarily absorb UV radiation. They just do it in different ways (BASF 2023):

Organic (Chemical) Filters	Inorganic (Mineral) Filters
Absorb UV via molecular interactions, converting UV rays into harmless heat	Act like semiconductors—their crystal structures absorb UV and release heat
Often come in smaller molecules, making them less visible on the skin	Larger particles can look more opaque (visible) on skin, but may also confer protection from visible light (via reflection/scatter)
Can also exist in particle or nanoparticle form, behaving a bit like inorganic filters	Micronization makes them more transparent and may improve UV absorption
Some degrade in sunlight (e.g., avobenzone), so they need stabilizers like octocrylene	More stable in when exposed to light; performance may vary based on particle size/formulation

The old paradigm of physical sunscreens reflecting and chemical sunscreens absorbing appears to be incorrect. It's possible if not likely, older formulations of physical sunscreens that utilized much larger particle sizes for which reflection/scatter was a more prominent part of the sun protection they afforded.

Chemical (Organic) vs. Mineral (Inorganic) : Which Is Better?

That’s the question you are here for—but, I don't have a direct answer. Most sunscreens contain the exact same ingredients and it really comes down to, do you want a sunscreen with organic ("chemical") UV filters or inorganic (mineral/"physical) filters. Most organic sunscreens currently contain all four of the most common organic filters: avobenzone, homosalate, octocrylene, and octisalate. Most inorganic sunscreens contain both inorganic UV filters: zinc oxide and titanium dioxide. Personally, I prefer and recommend sunscreens with inorganic UV filters, but that is primarily a preference based not entirely on scientific research (more on that in other parts of this series).

If you're looking to avoid certain UV filters due to concerns—such as potential effects on coral reefs or endocrine disruption—it's helpful to understand the role each ingredient plays in your sunscreen. That way, you can make informed choices to avoid specific filters while still achieving broad-spectrum protection, if that's your goal.

Common UV Filters and the UV Protection They Afford

Filter	UV Protection	Notes
Avobenzone (organic/"chemical")	UVA	Often paired with other filters to stabilize; not photostable on its own
Homosalate (organic/"chemical")	UVB	Common in U.S. sunscreens; under FDA review for systemic absorption
Octocrylene (organic/"chemical")	UVB	Helps stabilize Avobenzone; potential for skin sensitization; some questions over reef toxicity; can cause contact dermatitis (skin allergy)
Octisalate (organic/"chemical")	UVB	Often used to boost SPF and enhance water resistance; some questions over reef toxicity
Octinoxate (organic/"chemical")	UVB	Very common in daily-wear SPF; concerns over coral reef safety; occasionally causes contact dermatitis (skin allergy)
Oxybenzone (organic/"chemical")	UVB and short wave UVA(II)	Broad-spectrum, but under scrutiny for potential endocrine disruption; major concerns over coral reef toxicity; high rates of contact dermatitis (skin allergy)
Ensulizole (organic/"chemical")	UVB	Water-soluble; less oily—used in lighter formulations
Meradimate (organic/"chemical")	short wave UVA(II)	Weak absorber; usually combined with others
Zinc Oxide (inorganic/mineral/"physical")	UVB, UVA, and some visible light	Broad-spectrum; mineral filter with excellent photostability
Titanium Dioxide (inorganic/mineral/"physical")	UVB and short wave UVA(II), and some visible light	Mineral filter; gentle on sensitive skin; may leave a white cast

Notably, while concerns about certain chemical sunscreens—such as their potential to disrupt hormones or harm coral reefs—are valid, many may be overstated, lack strong scientific support, or have yet to be fully investigated (we will explore some of this in future parts of this series). It also has been demonstrated that some mineral sunscreens underperform in lab tests, possibly due to larger particle sizes that make them more effective at reflecting but less efficient at UV absorption, or because of greater consistency or ease of compounding chemical (organic) filters into products (my speculation). However, performance also depends on formulation, usage, and how the sunscreen is tested, so these reports may not be well-founded.

Conclusion

Choosing the right sunscreen doesn't have to be overwhelming—but it helps to understand what's actually in the bottle. While active ingredients are the key players in UV protection, many products use the same small group of filters, meaning your final choice often comes down to inactive ingredients, formulation, and personal preferences. Whether you lean toward organic (chemical) or inorganic (mineral) filters, the most important thing is finding a sunscreen you’ll actually use when you need it, and one for which you are comfortable with all the risks and benefits.

Dr. Ryan M. Trowbridge, MD, MS, MA

Harvard-Trained, Board-Certified Dermatologist and DermMythBuster

P.S. Have you come across any new or conflicting research on this topic? Please share—I’d love to explore it further with you!

For medical consultations with me, visit Bridge-Derm.com.

References

1. 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

2. BASF. Sun Protection: Absorption Is the Key Factor in UV Protection. BASF Personal Care. https://www.personal-care.basf.com/core-competencies/all-about-sun/sun-protection/absorption-is-the-key-factor-in-uv-protection. Published 2023. Accessed March 26, 2025.

3. Bolognia JL, Schaffer JV, Cerroni L, eds. Dermatology. 5th ed. Elsevier; 2024.