About

SunProtect.me answers one question — what sun protection makes sense today — from two inputs, and shows the arithmetic behind the second one. It sells nothing, recommends no product, and stores nothing about you.

Where the guidance comes from

Three sources, and nothing else. Every rule the calculator applies traces to one of them, and they are the first thing to check before changing any of it.

World Health Organization — ultraviolet radiation. The threshold this calculator turns on at, in WHO’s own words: “Sun protection measures should be used when the UVI reaches 3 or above.”
WHO, WMO, UNEP and ICNIRP — Global Solar UV Index: A Practical Guide (2002). The five exposure categories the UV slider is banded in: Low, Moderate, High, Very high and Extreme.
DermNet — skin phototype. The Fitzpatrick phototype describes how skin reacts to sunlight, especially burning and tanning, which is why the two questions here outrank the colour slider.
American Academy of Dermatology — how to apply sunscreen. The recommendation in full: SPF 30 or higher, water resistant, broad-spectrum; about one ounce — “roughly the amount to fill a shot glass” — for an adult; reapplied every two hours and immediately after swimming or sweating.

Also cited, for figures this site reports rather than implements:

Petersen and Wulf (2014), “Application of sunscreen — theory and reality”, Photodermatology, Photoimmunology & Photomedicine 30(2–3):96–101. The one figure this site cites from research rather than from guidance: in real use people apply about 20 to 50 per cent of the amount an SPF is tested at. It is why the calculator refuses to turn a factor into a number of minutes.
NHS — sunscreen and sun safety. Puts a whole-body adult application at 6 to 8 teaspoons — about 30 to 40 ml at a 5 ml teaspoon. The 30 ml this calculator uses is the bottom of that range.
Cancer Council Australia — sunscreen advice. Puts a full-body adult application at about seven teaspoons, and states the figure in millilitres: 35 ml.
European Commission Recommendation 2006/647/EC on sunscreen efficacy. Sets the European UVA standard the “UVA in a circle” mark stands for: UVA protection at least a third of the SPF, and a critical wavelength of at least 370 nm.
Skin Cancer Foundation — skin cancer in skin of colour. The basis for what this site says about darker skin: “For people of color, skin cancer is often diagnosed later, when it is harder to treat”, and “Regardless of skin color, sun protection measures are important to reduce the risk of skin cancer.”

What it will not calculate

There is no “safe time in the sun” anywhere on this site, and there never will be. Multiplying a factor by how quickly skin reddens produces a figure that looks precise and is not — it assumes a thick, even layer that stays put, and it turns a bottle into permission. The build refuses to ship it: a script checks every source file and every sentence the calculator can produce against a list of the phrasings that would say it.

That is not only a house rule. Sunscreen is tested at a standard thickness that almost nobody reproduces: measured in real use, people apply about 20 to 50 per cent of it. Any arithmetic that turns a factor into a number of minutes rests on the thickness nobody applies, which is why the number it produces is optimistic in exactly the situation where being wrong matters most.

It also makes no diagnosis and predicts no risk. The phototype shown is an estimate, labelled as one, with its confidence printed beside it — and where your two answers disagree, the page says so rather than picking a winner quietly.

How the guidance is kept honest

The UV Index decides the protection; the estimated skin type only changes the sentence of context beside it. That is not a promise, it is a test: the build asserts that for every UV Index and every activity, all six phototypes receive identical guidance. A change that gave darker skin weaker advice would fail before it could be published.

Who builds it

SunProtect.me exists because "what factor do I need?" has an answer that depends mostly on the UV Index, and almost every page that answers it is selling a bottle. This one takes two inputs, shows its working, and recommends no product at all.

Corrections are welcome and read first — see contact.