A UK airport wants to remind passengers of the rules they must follow when they pass through security. In a post shared on X , Heathrow Airport urged travellers to familiarise themselves with the rules about liquids stored in hand luggage. The alert said: “Good morning and welcome to Heathrow Airport. We hope you are looking forward to the weekend ahead of you! Remember, liquids should be under 100ml and in a clear bag when going through security.” GOV.UK explains that while some airports allow passengers to take liquid in containers that hold up to two litres of liquid, most airports do not let you carry liquids in containers larger than 100ml through security. The rules still apply if a large container is not full. The rules apply to all passengers at the airport; however, some exceptions may apply for items such as medicines, baby milk, or food for special dietary requirements. Heathrow Airport sets out its rules on a dedicated webpage on the airport’s website. The guidance explains: “Only limited quantities of liquids may be carried through airport security into the departure lounge. This includes bottled drinks, suntan lotion, fragrances, cosmetics, toiletries and all frozen liquids.” All liquids, creams, gels, pastes, and aerosols taken through security must be carried in containers of 100ml or less and fit inside one transparent and resealable bag no larger than 20cm x 20cm. When passengers arrive at security control, they will need to place this bag in the tray with their other items. The bag must be able to close properly when all of the liquid containers are stored inside it. Heathrow Airport states that liquids in containers over 100ml will not be permitted through security and should be packed in hold baggage. However, there are some exceptions to the 100ml rule. The guidance explains: “You are only permitted to carry quantities of liquid medication in excess of your personal liquid allowance where it is needed during the course of your flight. “All medication should be accompanied by documentary proof of authenticity, such as a prescription or letter from a medical practitioner confirming that you need them for your journey. Liquid medication that is not required on the flight should be carried as hold luggage.” There are also different rules for breast milk. The guidance explains: “Breast milk can be carried in the cabin; when it is stored in a clear, transparent container or bag. Flasks cannot be permitted. The volume of each container / bag should not exceed 2 litres. “Breast milk should be in a liquid format and not frozen. When travelling without an infant only breast milk can be carried in quantities greater than 100ml, this does not apply to formula milk or other baby juice / food.”