Guardian Beauty Store is a Terminal 2 outlet of Guardian, the pharmacy and health-and-beauty chain familiar across Singapore, found at #02-13, 60 Airport Blvd. in Changi Airport. It currently holds a 2.0 Google rating.
Airport pharmacies exist for the small emergencies of travel: painkillers before a long flight, remedies for an upset stomach, plasters, motion sickness tablets, sunblock, and the toiletries you had to surrender at security. A good pharmacist will do more than point at shelves, advising on minor ailments and checking whether a new medicine clashes with regular prescriptions, so it pays to ask rather than guess. Regular travellers know airport outlets tend to price a little above neighbourhood branches, so the sensible course is to top up essentials before you fly and treat the terminal shop as a backup rather than a first stop.
For passengers passing through Terminal 2, this is one of the last convenient chances to do exactly that before boarding.