Chemical leaveners, which came along in the 1800s, revolutionized how people cooked at home. They made possible not only quick breads such as baking powder biscuits, but whole new ranges of baked goods. They were a real time and labour saver at a time when, remember, women had to draw water and shovel coal or chop wood for their cooking needs before they could even start cooking.
Chemical leaveners work based on the combination of alkalines with acids. The chemical reaction releases carbon dioxide, which causes the baked good to rise.
The chemicals referred to are naturally-occurring chemicals and are 100% food-safe.