What it is and where it comes from
Collagen is the protein in skin, bones and tendons. Collagen powders and peptides are made from cattle hides, pig skin, chicken, or fish skin and scales, broken down into small pieces. Gelatin is a form of collagen.
Where you find it
Collagen powders and drinks, protein bars, beauty supplements and some yoghurts and sweets.
What to look for on the label
Look for "marine collagen" or "fish collagen", or a halal logo on bovine collagen. "Porcine" means pig.
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.