SPF 30 is the practical minimum for daily use. Higher SPFs offer diminishing marginal protection in ideal conditions, but real-world protection is usually much lower than the label suggests, so higher SPFs help.
The math on SPF numbers (in ideal application):
- SPF 15 — blocks ~93% of UVB
- SPF 30 — blocks ~97% of UVB
- SPF 50 — blocks ~98% of UVB
- SPF 100 — blocks ~99% of UVB
The jumps from SPF 15 to 30 are meaningful. From 30 to 50 is modest. From 50 to 100 is marginal in ideal conditions.
But real-world conditions aren't ideal. Diffey's research established that people typically apply about half the amount required to hit the labeled SPF. In practice, an SPF 30 applied at 50% concentration acts like an SPF 5-10. This is why some dermatologists recommend SPF 50+ specifically to give real-world protection in the SPF 15-30 equivalent range.
What to actually look for:
- Broad-spectrum — protects against both UVA and UVB. Not just UVB.
- SPF 30 minimum, ideally SPF 50 for face and neck.
- Adequate application — 1/4 teaspoon for the face, 1 teaspoon for the neck and chest.
- Mineral filters (zinc oxide, titanium dioxide) for sensitive or reactive skin. Chemical filters typically feel lighter and can be layered under makeup more easily.
- Iron oxides for visible-light protection, especially if you have melasma or hyperpigmentation.
Not more expensive = more effective. Formulation quality varies but a $12 drugstore SPF 50 can outperform a $70 luxury SPF 30 in real-world protection.