A sunscreen sold in two countries can carry different ratings, different symbols and sometimes different ingredients. The formula has not changed; the regulatory system around it has.
The main number describes one type of radiation
Sun protection factor measures how much longer skin takes to redden under laboratory conditions, and reddening is caused mainly by shorter ultraviolet wavelengths.
Longer wavelengths penetrate more deeply and contribute to ageing changes without producing the same immediate reddening, so they are largely invisible to that number.
This is why a high figure alone does not describe complete protection, and why separate indicators for the longer wavelengths exist alongside it.
Different regions grade the second range differently
Some markets use a star system, some use a plus-sign grade, and some require the longer-wavelength protection to be a fixed proportion of the main figure.
Each system is measured by its own test method, so the grades are not directly convertible between regions.
A product described as broad spectrum in one market may be tested against a different threshold than a product described the same way elsewhere.
Permitted filters vary by jurisdiction
Ultraviolet filters are regulated substances, and each region maintains its own approved list along with maximum permitted concentrations.
A filter widely used in one market may be unapproved in another, not because it is considered unsafe there but because approval requires a submission process that takes years.
Formulators therefore build regional versions of the same product, which is why an apparently identical bottle can have a different ingredient list abroad.
Classification changes what evidence is required
Some jurisdictions treat sunscreen as a cosmetic and some treat it as a regulated medicine or therapeutic good.
The classification determines what testing must be submitted, how claims may be worded, and how long approval takes.
Stricter classification tends to slow the introduction of new filters, while lighter classification allows faster reformulation. Neither arrangement is straightforwardly better.
Application quantity dominates the rating anyway
Ratings are established using a standardised quantity per area of skin, and that quantity is considerably more than most people apply in ordinary use.
Applying less does not reduce protection proportionally; the shortfall is steeper than that, so the number on the bottle overstates what thin application delivers.
Questions about sun protection in relation to a specific skin condition, medication or history belong with a qualified clinician rather than with a label comparison.