All image credit: Unsplash/Freepik
Look at the label whether it says ‘100% Cotton/Pure Cotton’ only then it is the original fabric.
Cotton fabrics often have a plain or twill weave, visible as a grid or diagonal pattern so look for it in the fabric.
Sprinkle a few drops of water over the fabric and see if the fabric absorbs water or not as cotton fabric quickly absorbs water while synthetic clothes repel it.
Cotton is prone to wrinkling, if the fabric wrinkles easily, it's a good sign of cotton.
A small piece of cotton will burn steadily, leaving gray ash with a paper-like smell. Synthetic fabrics might melt or have a different odor.