SkincareAddiction

OP is on feddit.de, sun can be a bit sparse over there.

Great comment!

Thank you for all the infos.

To get the advertised spf you’re supposed to apply about 1/4 a teaspoon per section of body

That depends on factors like the amount of skin you have in one part of the body (face – neck – legs etc.), which even in one area can vary greatly between individuals. Those recommendations are also kind of confusing sometimes as they might not tell you what exactly is meant (does "face" include the neck? What about the ears?). They're pretty diverse, too – some tell you to apply 1/4 of a teaspoon on your face, others say 1/2 a teaspoon for your face, head, and neck … In addition, you'd have to know what they mean by teaspoon: a metric teaspoon (5 mL), one teaspoon in the US customary system (about 4.93 mL, although that's (hopefully) reserved for culinary measurements), or a random teaspoon they found in their kitchen drawer? It's a mess.

SPF is tested at 2 mg per cm^2^, and this is also the amount that is used in most studies, so that might be your best bet to get the labelled protection. It's also one of the reasons why higher SPF is generally better as you could "get away" with applying a lower amount while not realistically sacrificing protection too much.

But good luck actually applying that much reliably consistently. I guess if you don't want to exactly measure the amount of skin on your face and the appropriate amount of sunscreen (even just once), just try to apply liberally? It's a really tricky process to communicate to consumers, which is why those approximate recommendations exist; otherwise, you might put a lot of people off using sunscreen altogether.