SPF, and the amount nobody actually applies.

For most people, across ten years, the sunscreen they actually wore will have done more for the condition of their skin than everything else listed on this site put together. We sell the everything else.

It changes where the money should go. Buying a vitamin C serum, a retinol and a course of treatments while wearing sunscreen occasionally is spending on the small levers and skipping the large one. It is an expensive way to stand still.

Skin varies, and nobody can tell you what your particular skin would have looked like either way. Nothing printed on a sunscreen label is a prediction about your face. What is true is that the evidence behind daily UV protection is older and less contested than the evidence behind anything else on the ingredients list, and that the obstacle is boredom rather than knowledge.

One thing this page does not cover. UV and skin cancer is a real conversation and not ours to have — it belongs with your GP and the Cancer Council. Everything below is about how skin looks and behaves.

The number on a sunscreen bottle is measured in a laboratory at a fixed density — two milligrams of product per square centimetre of skin. That density is not a suggestion. It is the condition under which the number is true at all. On a face and neck it works out at about a teaspoon, and most people apply between a quarter and a half of it.

The shortfall does not scale politely. Half the amount does not give you half the number; it gives you considerably less. An SPF 50 applied thinly is not an SPF 25 — it is a bottle whose label has stopped describing what is on your face. This is the most common reason sunscreen underperforms, and it costs nothing to fix.

The practical version, without the milligrams:

The standard advice is to reapply every two hours, and immediately after swimming, sweating or towelling. That advice is written for someone outside, and on a day spent outside it is right.

It is over-applied to office days. If you put sunscreen on in the morning, drove to work, sat inside, and are going home in the dark, the case for reapplying at two o’clock is thin. Nobody selling sunscreen will tell you that. Reapplication tracks exposure, not the clock — walking to lunch and back is not a Saturday at the beach, and treating them identically is how the habit gets abandoned as unrealistic.

Over makeup it is awkward and there is no elegant answer. Powders and sprays are easier to use than creams and much harder to apply at anything like the tested density. Better than skipping it, worse than the label suggests.

Australia regulates sunscreen more tightly than most countries do. A sunscreen sold here as sun protection is a therapeutic good, tested against the Australian and New Zealand standard. The claims on the front are not decorative; they mean defined things.

You will read everywhere that sunscreen is a daily, year-round, no-exceptions product. Published Australian guidance is more specific: sun protection is advised whenever the UV index reaches 3 or above. In Melbourne that is most of the year — and on many deep-winter days, it is not.

So the strict answer is that a grey July morning spent indoors is not asking anything of you. We would rather say that than overstate it. A rule people can tell is overstated is a rule they stop following in October as well.

The case for wearing it anyway is habit, not alarm. A daily routine survives; a conditional one asks you to check a forecast and decide every morning, and almost nobody keeps that up. Melbourne also produces 24°C in August without warning. Wearing sunscreen on a day that did not need it costs a few cents and thirty seconds.

Windows are the other half of the question, and the answer is smaller than the internet suggests. Ordinary glass stops most UVB and lets a meaningful part of UVA through. Car windscreens are laminated and block most of it; side windows generally do not. A desk against a sunny window, or a long regular drive, is a genuine exposure worth covering. An office with the nearest window four metres away is not.

If sunscreen is not happening daily and in the right amount, fix that before adding anything. Several of the other actives increase sun sensitivity while you use them, which makes the order matter.