How do you choose your sunscreen? Brand, packaging, price, a friend's recommendation, advertising, scent, texture, SPF, availability… All of these influence our choices, yet none is really the right criterion for an informed decision. By mechanism of action, sunscreens fall into two main types: mineral (physical) filters and chemical filters.
Chemical filters
Chemical filters are the more common on our market. Their active ingredient is absorbed by the skin; incoming UV rays are also absorbed and then neutralised by reacting with that chemical — so protection happens inside the skin (like stopping the burglar after they have entered the house). The chemical also depletes, so chemical filters must be reapplied according to their SPF.
A higher SPF extends the duration of protection, not its strength. If unprotected skin starts to redden in 5 minutes, SPF 4 extends that fourfold, to 20 minutes. Roughly, SPF 15–20 protects for up to an hour, SPF 30–50 for up to two hours. SPF 20 filters about 93% of UV, SPF 30 about 96%, and SPF 50 about 98% — no sunscreen is 100% effective. The biggest problem with chemical filters is that, with regular use, they can cause allergic reactions and make the skin oily and shiny.
Physical (mineral) filters
Physical filters form a molecular barrier on the skin and reflect incoming UV back. Neither the filter nor the UV is absorbed, and no chemical reaction occurs inside the skin. As long as they are not mechanically removed, their protection continues — they do not run out. These are actually the filters that should be preferred most, but until now they were less popular because they left a whitish cast on the skin. Molecular-scale refinements have solved that problem. One warning: stay away from nano-technology versions, since their very small size lets them be absorbed and can cause allergic reactions. Physical filters are also recommended for children.
What about vitamin D?
Will protecting from the sun lower our vitamin D? Yes, to a degree, because the best hours for vitamin D synthesis are 11:00–16:00 — exactly when it is advised to avoid the sun or apply good protection. The solution: on an average day, exposing the hands, face and arms for 20 minutes meets the daily ~1000 IU vitamin D need; on sunless days, oral supplements (600–800 IU, with some recommending up to 2000 IU) are advised.
The hands and face are the most continuously sun-exposed areas, so their skin ages, sags, develops spots and wrinkles far faster than the rest of the body. These are the parts that need constant protection. If you want vitamin D from the sun, protect the hands and face well and leave the rest of the body exposed for 20 minutes — there is no need to extend that, since vitamin D synthesis reaches saturation and stops increasing no matter how long you stay.
Our recommendation
We recommend choosing a physical filter. If you will wear sunscreen on your face year-round, these are the best option; for body protection in summer you can also choose combined or chemical filters. Products worth recommending include a non-whitening mineral filter (Medik8 Physical Sun-Screen), a combined sunscreen containing both physical and chemical filters (Obagi), and a chemical filter with added active ingredients tailored to different skin types and concerns (Solenta).
