What it is and where it comes from
Propylene glycol is a man-made liquid used to carry flavours and colours and to keep food moist. Chemists call it an alcohol, but it is not the alcohol in drinks and does not intoxicate. It is not made from animals.
Where you find it
Flavourings, food colours, icing, cake mixes and soft drinks.
What to look for on the label
Nothing to check for halal. When it carries a flavouring, the flavouring itself is a separate question.
This is a guide, not a fatwa. Recipes change, so check the label, look for halal certification, and ask your local imam where scholars differ.