What Product Offers the Highest Sun Protection?

Verina asks…Dear Beauty Brains, you bring rationality to the cosmetics industry, a feat which deserves the Nobel Prize, along with my undying gratitude. 

I am trying to find a cream or primer to use under makeup that offers the highest sun protection available. I am considering mainly mineral sunscreens, since many of the chemical ingredients irritate my skin. I have narrowed it down to:

MAC Prep+ Prime (SPF 50 with active ingredients: zinc oxide 16.10%, octinoxate 7.50%)

Fasio Zero Expert UV Primer (SPF 50 with active ingredients  ethylhexyl methoxycinnamate 7.49%, phenylbenzimidazole sulphonic acid 2.50 WW%, zinc oxide 15.36 WW%.) 

I await your words of wisdom…..and what the hell kind of sun protection is phenylbenzimidazol sulphonic acid?

Alchemist responds (from the Beauty Brains Forum): 

It’s impossible to tell which actually provides more sunprotection from the active ingredients, especially when they are so close in composition (ethylhexyl methoxycinnamate & octinoxate are the same thing, the first one is the INCI name, the second is the USA drug name). SPF is very heavily influenced by the other ingredients in the formulation and production methods. The type and size of the Zinc Oxide will also have a big effect. Given that both claim SPF 50 both must have a tested SPF of 50 or above.

Phenylbenzimidazole sulphonic acid is better known in the USA as ensulizole. It’s a water soluble UVB sunscreen that is neutralised in situ (usually with TEA or Sodium Hydroxide)

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