SPF Is the Anti-Ageing Step Almost Nobody Gets Right

A short, blunt note on the single most under-used product in British bathrooms.

The number that changes the conversation

Most photoageing research puts the figure somewhere between 70 and 90 percent. That is the share of visible ageing on the face — pigmentation, fine lines, loss of elasticity, broken capillaries — that comes from cumulative UV exposure, not from genetics or time. The implication is uncomfortable: a great deal of what we treat in clinic in our forties and fifties was technically preventable in our twenties and thirties. SPF is the closest thing aesthetics has to a daily medication.

What 'broad spectrum' actually means

A proper sunscreen protects against both UVB (the burning rays) and UVA (the ageing rays that pass through cloud and glass). On a UK label, you want a high SPF and a high UVA rating — ideally the UVA-in-a-circle symbol, or four to five stars under the Boots system. A product labelled only 'SPF 30' tells you nothing about UVA. This matters because in the UK we get plenty of UVA year-round, even when the sky looks miserable.

How much you are actually applying

The single biggest reason SPF underperforms is dose. The studies that produce that lovely SPF 50 number assume you are applying two milligrams per square centimetre of skin — which works out at around two finger-lengths of product for the face and neck. Most people apply a quarter of that. If you are using SPF 50 at a quarter dose, you are getting somewhere closer to SPF 12 in real life. Apply generously, twice if you are out for long.

Reapplication, and why your morning makeup is not the problem

SPF degrades with UV exposure and sweat. If you are commuting, working indoors near a window, and going home — your morning application is broadly fine. If you are outside for any length of time, reapply every two hours. Powder, spray and stick SPFs exist precisely so you can do this without ruining makeup. Keep one in your bag.

Mineral or chemical, and does it matter?

Mineral filters (zinc oxide, titanium dioxide) sit on top of the skin and reflect light. They tend to leave a white cast — fine on fair skin, often a problem on deeper tones. Modern chemical and hybrid filters protect equally well and disappear on every skin tone. I prescribe both. The best SPF is the one you will actually use every day — elegant texture, no white cast, no stinging eyes.

What I would have told my 25-year-old self

Wear it every day. Indoors counts. Reapply. Use enough. Pair it with a daily antioxidant serum (vitamin C in the morning, before SPF) and you have built the entire foundation of an anti-ageing routine. Everything else — retinoids, facials, lasers, microneedling — is an upgrade on top of that. Without SPF, the upgrades are working against a tide they cannot win against.