Bread is generally made from wheat, which contains the protein gluten.
For this reason, all wheat-based breads are a bad idea for people who have celiac disease or gluten sensitivity.
However, most commercial breads are unhealthy, even for people who do tolerate gluten.
This is because the great majority of them are made from refined wheat, which is low in essential nutrients (empty calories) and leads to rapid spikes in blood sugar.
Alternatives: For people who can tolerate gluten, ezekiel bread is an excellent choice. Whole grain bread is also definitely better (or “less bad”) than white bread.