A very short message (9 words) was posted on Facebook: "Stop doing your skincare routines on board; it's a 2-hour flight." This comes at a time when it's like a trend to be applying moisturisers, face masks and eye creams on short-haul flights.

The reasoning is, of course, that the cabin humidity is so low (it can be 20% below normal) that your skin will go dry.

The post went straight over the top with a flood of ironic comments. A number of passengers actually asked whether the airline was about to introduce a charge for applying make-up on board, or indeed whether they were going to start selling face masks on board at €9.99.

A few others took the chance to level a withering critique of the airline's rigour in enforcing carry-on size at the gates. Others, of course, were just having a good laugh at the need to be presentable for the first thing you do upon landing.

Despite the fact that these routines are very much in vogue in the cabin, dermatology and skincare experts would advise that you do your facial before you get on the plane.

The technical advice issued by London Luton Airport (by Dr Nora Jaafar) is that you should avoid any complex skincare treatments at 40,000 feet. If you do do any at all, then it should be confined to something very simple such as a hydrating mist or a lip balm.

People must have clean hands and avoid anything that's going to be a bit of an irritant in the low humidity. That's another one of the perennially controversial on-board behaviours (alongside the early occupation of the boarding area, reclining, the rush to stand as soon as the seatbelt sign goes off, etc.).

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