Approved UV filters are separated into 2 categories: organic chemistry (organic meaning carbon-based); and inorganic chemistry (mineral-based metal oxides such as zinc oxide or titanium dioxide).
So, what are the real differences between “chemical” sunscreens using organic chemical filters and “mineral” sunscreens using inorganic chemical filters? Let’s check the science.
Physics Reminder
A white paint will predominantly reflect visible light and scatter (dampen down) UV rays, and that was the principle of the white zinc paste that has been historically used in Australia.
Scientists developed nano-sized or nano-structured metal oxides that do not reflect visible light and can therefore be used to produce transparent sunscreens. These nano-engineered particles act more like typical organic UV filters by predominantly absorbing UV rays.
“Chemical” and “mineral” sunscreens are therefore not that much different from a mode of action viewpoint.
The benefits of mineral sunscreens include:
- Stable: unlike some organic UV filters, inorganic UV filters are not degraded by UV rays.
- Big enough: inorganic UV filters, even nano-sized, are much larger than the older generation organic (carbon-based) UV filters and are just too big to go through the skin.
- Milder: there is a lesser chance of allergic reaction to inorganic UV filters in general (but allergy to zinc oxide is possible too).
Limitations of mineral sunscreens include:
- Reactive: inorganic UV filters can be photo-active and can generate reactive oxygen species that may deteriorate some coatings.
- Harder to apply correctly: mineral sunscreens (especially those using high concentration of zinc oxide) can be pasty, making it harder to apply consistently and achieve label claim.
In summary, mineral sunscreens can be a solution for those with sensitive skin or those concerned by the penetration of some organic UV filters into the skin.
But remember that, like all sunscreens, mineral sunscreens need to be applied with the approved dose of 2mg/cm2 (about 5g for the face or 35g for a full body application) to achieve the sun protection claimed on label.