Buyers must prioritize SPF (Sun Protection Factor) and PA ratings (e.g., PA++++) to ensure broad-spectrum protection against both UVA and UVB rays. Key technical attributes include water resistance duration (typically 40 or 80 minutes), photostability of active ingredients, and the distinction between physical blockers (Zinc Oxide, Titanium Dioxide) and chemical filters (Avobenzone, Octocrylene). For high-end markets, ensure the formulation is non-comedogenic, paraben-free, and dermatologically tested.