New rules permitting small amounts of liquids in hand luggage on European and UK flights have come into effect.
Liquids are limited to 100ml per container and no more containers than would fit in a one-litre plastic bag.
The new EU-wide rules represent a relaxation of the anti-terror measures in the UK, but will represent a clampdown for many European countries.
The UK imposed curbs in August after police said they had foiled a plot to bring down as many as 10 planes.
The measures were not adopted uniformly elsewhere in the EU, with many travellers previously facing much stricter restrictions on carrying liquids out of the UK than they did on their return from an EU country.
Now passengers across the EU and in Switzerland, Norway and Iceland will be able to carry drinks and toiletries through airport security, but only in small amounts.
Airport officials say staff have been undergoing training and are on duty to advise people in check-in queues about the latest changes.
While restrictions on hand luggage sizes brought in at UK airports in August were relaxed the following month, most liquid items have been banned from hand luggage until now.
Some European countries introduced similar regulations, but now all 25 EU countries, plus Switzerland, Norway and Iceland, will have to impose the same rules as minimum standards. Countries can use even tighter rules if they wish.
The new rules require the liquid containers containing items such as toothpaste, cosmetics and shaving foam be carried in a clear plastic, re-sealable bag that does not exceed 20cm x 20cm (8in x 8in).
100ml containers in one-litre re-sealable clear plastic bag (20cm x 20cm)
Verified prescription medicines essential for flight
Baby milk and liquid baby food
At the airport security search, the plastic bag will need to be removed from the hand luggage and X-rayed separately.
The new rules also mean essential medicines and baby food are allowed in amounts larger than 100ml.
However, passengers will continue to be able to buy perfumes, cosmetics, bottles of alcohol and other drinks in the departure lounge after passing through airport security.
"The new rules do not limit the liquids that you can buy at shops located beyond the point where you show your boarding pass or on board an aircraft operated by an EU airline," said the European Commission.
Travellers have to remove jackets and coats, and take large electrical items like laptop computers out of their luggage for separate scanning.
Large musical instruments are also permitted, in addition to one item of cabin baggage, Britain's Department for Transport has said.
Gatwick Airport said the new rules were slightly delaying passengers as pass through security checks.
A spokeswoman said: "It's taking a little longer for passengers to get checked in and to pass through security to the departure lounge today.
"It's taking about 45 minutes to an hour - about half as much time again as it would normally take."
Heathrow Airport operator BAA reported slight flight delays but said they were mainly down to fog.
A spokesman said: "There has been fog both in the UK and in Europe today and this has caused some of the delays, including some flight cancellations."