But now an Italian airport has decided to waive the 100ml maximum limit - as long as the liquid is pesto.
More than 500 jars have made it through since Genoa's Cristoforo Colombo airport launched the "Il pesto Ã¨ buono" (Pesto is good) scheme on 1 June.
The cost? A donation to Flying Angels, which flies sick children abroad for treatment.
Pesto - a popular pasta sauce made with basil, cheese, and pine nuts - is a local speciality in Genoa.
The airport said the brainwave arose after staff were faced with "hundreds of jars that were seized in airport security checks".
Tourists with pesto jars of up to 500g can ask for a special sticker in exchange for a â‚¬0.50 (Â£0.44; $0.55) charity donation - although the airport says many are donating more.
The pesto is then scanned in a special x-ray machine before proceeding onto the plane as hand luggage.
Foreigners are not the only ones grateful for the pesto-preserving initiative. According to the airport, Genoese travelling out of Italy are delighted to find they can take the much-loved foodstuff along.
There are some rules, however: Passengers can take either one 500g jar, or two jars up to 250g. They must be flying directly from Genoa.
And crucially, the pesto must be Genovese.
In an era of high-security air travel, many a passenger has fallen foul of the rules banning liquids on planes.