What it is and where it comes from
Lactose is the natural sugar in milk. It is made by crystallising it out of whey and washing it. Halal certifiers accept it, since it is a pure sugar separated from the milk.
Where you find it
Tablets and medicines, baby formula, sweets, chocolate, bread and seasonings.
What to look for on the label
Nothing to check for halal. People with lactose intolerance should avoid it.
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.