Sunscreen SPF Formulation FAQ: SPF, PA, and Broad Spectrum

What do SPF and PA mean?

SPF, or Sun Protection Factor, measures protection against UVB, the rays that burn the skin; it is roughly the multiplier for how much longer skin can be exposed before reddening compared with no protection. PA, short for Protection Grade of UVA, is a rating system for UVA protection shown with plus signs, where more pluses mean stronger UVA defense. A sunscreen can have a high SPF but weak UVA protection, so check both numbers and the broad-spectrum claim before you trust the label.

What does broad spectrum mean?

Broad spectrum means the product protects against both UVB and UVA. UVA rays penetrate deeper and are associated with premature aging and pigmentation, while UVB is linked to sunburn, and both contribute to skin cancer risk. In the US, a sunscreen must pass specific testing to carry the broad-spectrum label, and in the EU and other markets UVA protection is linked to the SPF level. For real-world coverage, choose a broad-spectrum product and apply enough of it.

What is the difference between mineral and chemical filters?

Mineral filters, mainly zinc oxide and titanium dioxide, sit on the skin and scatter or absorb UV; they are broad spectrum and generally well tolerated but can leave a white cast. Chemical filters absorb UV energy and convert it into heat; they spread easily and feel lighter but are more likely to cause sensitivity in some people and have faced more regulatory scrutiny in recent years. Many modern formulas blend both types to balance protection, feel, and cosmetic elegance.

Why do some sunscreens pill or feel greasy, and how is that fixed?

Pilling and greasiness come from how the filter system and film formers interact with skin and with other products. High filter loads, poorly matched oils, and incompatible thickeners cause balling, while heavy emollients cause shine. Formulators fix this by balancing the oil phase, choosing film-forming polymers that dry down smoothly, and testing the product over moisturizer and makeup. Ask your manufacturer for wear tests, because a sunscreen only works if people actually apply the right amount.

How is SPF tested and how do I make compliant claims?

SPF is measured by standardized in vivo testing methods recognized by regulators, such as ISO 24444 internationally and the FDA's testing procedures in the US, and water-resistance claims have their own dedicated protocols. Regulators also maintain lists of approved UV filters that differ by country, so an ingredient that is legal in one market may not be in another. Work with a laboratory that runs the required test method for each target market and never guess a number for the label.