You know the routine: belt in one tray, laptop in another, and that bottle of serum that absolutely will not fit in the clear plastic bag. Two security gates later, there it is, lit up under the lights — the beauty shop, right by the departure gate. You go in to kill five minutes and come out with a mascara and a vague sense of having been clever.

You're the beauty adviser now

In a city-centre beauty hall, someone always ends up asking whether you need a hand. At the departure gate, that someone is a rare sight: open shelving, testers sometimes picked clean, and there you are comparing two foundations under a concourse strip light at six in the morning, with skin that has spent the night against a synthetic leather seat. Good luck with that diagnosis.

A traveller comparing two foundations in an airport beauty shop
The diagnosis is yours to make, not the sales assistant's

So the advice is on you. Know your shade, your preferred texture, the active that makes your skin flare — or the one you avoid. It rewards the organised and punishes the impulsive, which is more or less the story of airports generally. What you lose in service you gain in peace: nobody is going to press a "global anti-ageing" serum into your hands on the grounds that you look tired.

Travel formats: handy, or small-print maths

A shop past security lives with a rule a city pharmacy doesn't: liquids in cabin baggage are still restricted in the UK, generally to containers of 100 ml or less, and the rules vary by airport — check before you pack. Hence shelves built for a cabin bag: minis, gift sets, 30 ml bottles, solids. A shampoo bar or a stick balm slips through more easily than a litre of cleansing milk, and it's often a good way to try a brand in travel form before committing.

Watch the trick, though: a mini is about convenience, not value. Per millilitre it almost always costs more than the full size, and there's a lot of packaging for very little product. If you have the choice, a refill or a solid will do the same job with less waste in your wash bag. The question to ask in front of the display: am I buying a format, or an excuse?

Airport exclusives: real, or just a nice word?

"Airport exclusive" is everywhere, and it does have an effect, let's be honest. Sometimes it earns its keep: a shade, a set or a size sold there and nowhere else. When that's true, it's a genuine exclusive. Other times it simply means a bundle put together in-house — two products in a pretty box, at a price that climbs faster than the contents are worth.

The question is simple: would you have bought this product if it hadn't come in the box? If the answer is no, you haven't bagged a bargain, you've just bought something. The cardboard recycles; the guilt, less easily.

The phantom discount that sails through customs

Duty-free doesn't necessarily mean cheaper, and that may be the most profitable misunderstanding in the terminal. Depending on where you're flying and the retailer's duty-free status, some taxes may be reduced, but that's no guarantee of a lower shelf price — and duty-free rules don't apply to every journey, so check rather than assume. As for the crossed-out price, it tells you more about how a brand positions itself than about what you're saving.

The real trap isn't the price, it's the basket. Saving £15 on a £60 treatment you had no intention of buying is another way of spending £45. A tired brain and a duty-free shop make excellent company; your bank balance, rather less so. Do the maths while your head is still clear, before the till: how many products have come into your life through an airport and never left it?

Budget

Prices for a mini, a serum, a gift set or a shampoo bar vary too much by brand, line and retailer for a single range to be honest. The airport is genuinely useful for a rescue buy and for travel sizes; for anything you repurchase exactly, a pharmacy, supermarket, beauty retailer or the brand's own site is easier to compare. Labels differ enormously from one terminal to the next, too — be wary of generalisations, including mine.

Three questions before the till. Do I already know my shade and my texture? Would I have bought this in town, at this price? And will it fit the cabin liquids limit — or into a cabin bag that's already full?

One obvious thing gets forgotten somewhere around the security trays: this isn't a shop, it's a corridor. Time is short, the lighting is poor, and nobody is going to catch you if the shade is wrong. If you've only got five minutes before boarding, spend them on a coffee and a last look at your boarding pass: the serum will wait for you perfectly well in town.