1. SPF 30 or higher
2. Broad spectrum
3. Water resistant
But why and what else?
FYI, you can just end here (check out the beautiful infographic by informationisbeautiful).
SPF 30 or higher
SPF is a measure of how much your skin can take before burning. SPF 30 means protection from around 97% of UVB rays. Back in 2017, the Philippine Dermatologic Association advised at least SPF 15 but the amount of protection of SPF 15 is around 93% while SPF 30 gives around 97. SPF 50 gives you around 98% and the difference between that and anything higher gives you a very little increase.
Unfortunately, while sunscreens are tested at 2mg/cm2, most people only apply a fraction of that amount, meaning the actual SPF you get is a fraction of that amount, with probably patchy coverage (especially if you don't remember your hairline, ears and neck). I personally prefer SPF 50 to make sure that even if my layer is thin, I'm getting somewhere around the 30 mark.
And no, sun protection does not layer (SPF 15 sunscreen + SPF 15 foundation = SPF 15 or less in reality). And if you layer on top of your actual sunscreen, make sure you leave it on enough for the sunscreen to dry and to pat whatever it is on top else you will be rubbing off your sunscreen. Don't rub/touch your face either! However, there might be some benefit in using 2 layers of sunscreen. Think of it as like applying two coats of polish instead of one to fill in the area properly.
Years ago, I also posted about using FTUs (finger tip units) as a way of measuring how much sunscreen to use. However, I realize that this will not work for ALL sunscreens (especially asian ones) as this will probably work only for denser sunscreens which tend to hold together more as asian sunscreens tend to be on the runnier side, and as FTUs are based on 5mm nozzles. Luckily, lab muffin experimented on finding the surface area of her face (not including her ears and neck?) and her results showed that her 381cm2 of her face alone required 60% of the normal 1/4 teaspoon recommendation or around 0.76 mg or ml of product. If talking about FTUs, which for an adult (probably caucasian) female, an application of 2 FTUs will be for her face leaving a measly 0.5 FTUs for the neck... which doesn't seem quite right for the amount of area for the neck.
I think, therefore to revise my estimates of FTUs and surface areas depending on the person. While information is beautiful shows a good estimate, personally, as a tiny asian, my entire head area would give me around 9 hands or 4.5 FTUs and that my neck, ears and what is under my chin is equal to a bit more than half of that. I would therefore probably need around 1.6 - 1.8 mg or ml of product or a bit under half a teaspoon of product for the entire area. This is a bit less than the 2 fingers/5-6 FTUs/2ml+ worth shown by information is beautiful (which I learned about after FTUs. Which could have made my life easier as 2.5 FTUs would be generally adequate versus 5-6 fingers which would generally be optimal.). After all, better safe then sorry!
And this doesn't even add your décolletage QAQ
This especially emphasizes that you should really layer your protection. Aside from adequate sunscreens, add a lipbalm, umbrella, hat, closed shoes, clothes and sunglasses (the only way to shield your eyeballs!). Bonus points for fabrics with UPF 30!
Broad Spectrum
So did you know that your sunscreen should protect you against UVA and UVB? Yes, that's why you need a broad spectrum sunscreen! But did you know that sunscreen should protect you against UVA1, UVA2 and UVB which are all different wavelengths... and not all "broad spectrum" sunscreens protect against all 3 necessarily... Because UVA protection is a relatively new term such that wikipedia doesn't label the difference in sunscreen ingredients. Fortunately... the miracle that is skinacea does, it's a better version of skincancer.org's. UVA protection is measured as PPDs (Persistent Pigment Darkening) or PAs or stars. This tells you how much more UVA exposure your skin can stand before darkening. I use PAs because Japanese sunscreens use them, so there! BUT PA++ gives you anywhere from 4-8 PPDs...I would recommend PA++ for cooler times and PA+++ for tropical countries and summers... but sometimes I do like to live dangerously with a PA++ myself (and sometimes not at all! But don't follow that 0.0).
Still, your best bet for a single ingredient sunscreen that is actually broad spectrum is either zinc oxide or Tinosorb S or M. Most sunscreens in the Philippines contain a combination (as with the two above) so check if it's actually broad spectrum using the ingredients list and the internetz. Or live dangerously!
Water Resistant
Humans sweat. They also sweat a lot during summer! This is why sunscreen should be reapplied. Water resistant sunscreens stay on the skin longer, for at least 40 minutes... but the hotter it is, the more you have to reapply. I apply my sunscreen before sun exposure (after all my skincare). I should reapply after 20 minutes of sun exposure then around four to five hours after (based on an SPF of at least 30 PA+++). This is why I always have a tube of sunscreen in my handbag. But I really don't unless it's high summer or depending on how good the sunscreen is at sticking to my skin. I also have to reapply once I swim, sweat a lot or do outdoor sports (lol) because sunscreen won't last that long.
I am the type of person to NOT apply sunscreen when I'm just at home or it's cloudy out. It's a great excuse to get your Vitamin :D
Japanese sunscreens have separate formulations for sports or for daily use. However, Japanese (and Korean) sunscreens prefer the newer chemical filters which FEEL great but may be BAD for the environment. Please do not use these in places with marine life. They say oxybenzone is the culprit, but let's err on the safe side. Use a good old physical, reef safe product at the beach.
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