SPF Decoded: Mineral vs Chemical Filters

Two mechanisms of protection

Sunscreens work in one of two ways: by physically blocking radiation at the skin's surface, or by chemically absorbing UV energy and converting it to low-grade heat. Both are valid; the choice depends on skin type, use case and personal preference.

Mineral filters

Zinc oxide and titanium dioxide sit on the skin and reflect or scatter UVA and UVB radiation. They are:

• Immediately effective: no wait time.
• Photostable: they do not degrade in sunlight.
• The safest choice for reactive, post-treatment, pediatric and photosensitive skin.
• Broad-spectrum by nature: zinc oxide covers the full UVA and UVB range.

The historical drawback, a white cast, is largely resolved by modern micronised and nano formulations, though darker skin tones may still see it.

Chemical (organic) filters

Avobenzone, octocrylene, homosalate, and the newer Tinosorb and Mexoryl absorb UV and dissipate it as heat. They tend to feel lighter, wear invisibly and layer well under makeup. Caveats:

• Some older filters (oxybenzone, octinoxate) are less photostable and more allergenic, and face regulatory restrictions in several markets.
• They require ~15 minutes to activate.
• Newer generation filters (Tinosorb S, Tinosorb M, Mexoryl XL) are photostable, broad-spectrum and well-tolerated.

Which to choose

• Reactive, post-treatment or children's skin → mineral.
• Daily wear under makeup, oily skin → a modern chemical or hybrid.
• Extended sun exposure → whichever you will actually reapply.

The best SPF is the one you wear every day, generously, and reapply through exposure. SPF 50, broad-spectrum, applied in two finger-lengths and reapplied every two hours of sun, is the non-negotiable, the filter type is the secondary decision.