Sunscreen is the most evidenced product in skincare and the one people are least consistent with. Most of the reasons for that are practical rather than clinical: the texture is wrong, the amount is wrong, or it was chosen for a beach holiday rather than a Tuesday.
Here is how to choose one, and what actually matters.
The number matters less than the amount
SPF is tested at 2mg per square centimetre of skin. Almost nobody applies that much. Most people apply between a quarter and a half of it, which means a bottle labelled SPF50 is delivering something closer to SPF15 in real use.
The practical rule is roughly two fingers’ length of product for face and neck. If that seems like a lot, that is the point.
UVA protection matters as much as SPF
SPF measures protection against UVB, the wavelength primarily responsible for burning. UVA penetrates more deeply and contributes to photoageing and pigmentation, and it passes through window glass.
In the UK, look for the UVA logo in a circle, or a star rating. Four or five stars is what you want. A high SPF with poor UVA protection is a half-finished product.
Chemical or mineral
Chemical filters absorb UV and convert it to heat. They tend to be lighter and cosmetically more elegant.
Mineral filters, zinc oxide and titanium dioxide, sit on the surface and reflect UV. They are generally better tolerated by reactive skin and are the standard recommendation after a procedure or while a barrier is recovering.
Neither is safer or more effective in general. The right one depends on your skin and what you will actually wear.
Texture is a clinical consideration, not a vanity one
The best sunscreen is the one you use daily. If a cream feels heavy on oily skin, use a fluid. If a fluid feels drying, use a cream. Changing format solves more adherence problems than changing brand.
What about pigmentation
If you are treating melasma specifically, visible light also contributes, not only UV. Tinted formulations containing iron oxides offer some protection against visible light that clear formulas do not.
What we would tell you at the counter
Wear it every day, all year, including when it is grey. Use more than feels necessary. Reapply if you are outdoors for long periods. And if you are using retinoids, acids or vitamin C, treat sunscreen as part of that routine rather than as a separate decision, because without it you are paying for actives that will not deliver.