New airport baggage rules that allow limited amounts of liquid to be carried on flights in hand luggage come into effect today.
Applicable at all UK and EU airports, the new regulations permit passengers to carry on board such items as shampoo, toothpaste and shaving foam as long as they do not exceed 100ml (about four fluid ounces).
Heathrow airport officials said extra staff would be on duty to go along check-in queues advising passengers of just what can and cannot not be carried on board.
British Airways and other airlines have been emailing customers informing them of the new regulations.
Since the thwarting last August of alleged plots to blow up aircraft, liquid items have not been allowed to be carried through security in hand luggage at UK airports.
Somewhat confusingly, UK passengers travelling from some European countries to the UK in recent weeks have not faced restrictions on liquids.
Now, regulations have been standardised across the EU, with the new rules also applying to airports in the non-EU countries of Switzerland, Norway and Iceland.
Allowable items, subject to the 100ml size restriction, include suntan lotions, perfumes, hair gel, mascara, lip gloss and soft drinks.
All liquid containers must be carried in a separate, clear plastic, zip-top or re-sealable bag that does not exceed 20cm x 20cm (8ins x 8ins or one litre capacity).
Items must fit in the bag comfortably, and the bag must be completely closed.
At the airport security search, the plastic bag must be removed from the cabin bag and X-rayed separately.
A Heathrow airport spokesman said; "We have drafted in extra staff to cope with the new requirements, and we have also been recruiting extra security staff recently.