When purchasing for cosmetic applications, you must prioritize purity and particle size. Ensure the product is Cosmetic Grade (not Industrial) with a purity level of at least 99.0%. For sunscreens, look for Nano-grade (10-100nm) for transparency, while for color cosmetics like foundations, Pigment-grade (200-300nm) is required for high opacity and whiteness. Additionally, verify the surface treatment (e.g., Alumina, Silica, or Stearic Acid) which determines the powder's dispersibility in oil or water phases.