SPF & the ISO sunscreen standards (ISO 24444, 24442, 24443)

SPF is not a vibe. It’s a measured number, and there are international standards for how to measure it.

  • ISO 24444, the in-vivo test for SPF (UVB protection), measured on real human volunteers
  • ISO 24442, the in-vivo test for UVA protection
  • ISO 24443, the in-vitro (lab instrument) method for UVA protection, used for the “PA+” and “broad spectrum” claims

Why it matters: anyone can print “SPF 50” on a tube. The question is whether the number came from an actual ISO-standard test at an accredited lab, or from the design software. Independent testing of sunscreens in several countries (including India, quite publicly) has repeatedly caught products delivering half their labelled SPF or less. Pakistan has no routine independent SPF verification, so the test report is the whole game.

What we ask brands: which standard, which lab, and can we see the certificate. If a sunscreen on BYOUT carries an SPF claim, that’s because we’ve seen the paperwork, and the stamp on the product page links you right back to this explanation.

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The BYOUT Library is educational content, not personalised medical advice. For persistent or severe skin concerns, a dermatologist beats any article, including ours.