Just SPF isn't enough, you also need PA protection. SPF Protects you from UVB rays, which cause sunburn, redness and skin cancer. PA Protects you from UVA rays, which reach deeper into your skin layers and cause long term skin damage, such as aging, wrinkles and DNA damage. PA is based on how long the product prevents you from getting tanned. On average, the human skin will start to tan within 1-2 hours, so you'll need to get a product based on your needs. For the super careful (or paranoid), even if you're indoors all the time or wear long sleeves you'll need to apply sunscreen because UV rays can penetrate through most materials.
For anyone curious, I struggled with finding a good sunscreen until I finally started using things called sun milk or essence, which is a more watery version but it absorbs into the skin fairly easily and without any of that annoying oily residue. I recommend MISSHA's sun milk or Etude House's Sunprise Mild Airy Finish. Oh, and for most sunscreens, you need to wait 15-30 minutes before it's fully absorbed into your skin so that it actually works. You can't just apply it and head off like what the maiko are doing! Of course, you'll need a good cleanser too in order to wash them off at the end of the day. Remember to reapply sunscreen through the day!