Every figure on a sun protection label is the answer to a question narrower than the one people ask
SPF, the UVA circle, the star rating and the protection categories. What each measure is a measure of, what it is not, and the conditions each one assumes.
What SPF is a measure of, and precisely what it is not
SPF is a ratio produced by a defined laboratory test against one specific effect of ultraviolet radiation. It is not a percentage, not a duration and not a measure of everything the sun does.
Definitions · 11 minWhy SPF and protection are not proportional, and how that gets misrepresented
Doubling the number does not double the protection. The relationship is a reciprocal, the difference between high figures is small, and the way that is presented in retail and advertising is where the misleading happens.
Definitions · 11 minThe UVA circle and the star rating, and why they answer different questions
One is a pass mark tied to the labelled factor, the other is a ratio expressed in bands. They look like alternatives on a shelf and they are not comparable measures.
Definitions · 11 minThe application quantity the SPF number assumes, and what changes when less is used
Every printed factor was measured at two milligrams of product per square centimetre of skin. Applying less does not reduce protection in proportion. It reduces it faster, and the mechanism is worth understanding.
Definitions · 12 minBroad spectrum: what the phrase requires, and where it requires nothing at all
In the United States broad spectrum is a defined term with a test behind it. In the United Kingdom it is not defined in the same way, which changes what the same two words mean on a pack.
Definitions · 11 minLow, medium, high, very high: the categories and why labels stop at 50 plus
Behind the numerals sits a set of four category words and a recommended list of permitted figures. The scale stops at 50 plus, and the reasoning for the cap is worth reading.
Definitions · 11 minThe wording note
One email a fortnight on sun protection claim language: what changed in the codes, what a published ruling turned on, and one phrase examined in full. Written for people who write, approve or check labels and advertising. Unsubscribe whenever you like.
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