Olive Young is in Terminal 1 (272 Gonghang-ro, B1) and Terminal 2 (446 Je2terminal-daero, B1), 6am–10pm, before check-in. The Aqua Fresh sunscreen (50ml+20ml) has 3.4K+ reviews; both tubes are under 100ml, so they can go in your carry-on in a 1L clear bag.