Acrylic nails involve mixing acrylic powder with a liquid and applying the mixture to the nails; it hardens with exposure to air. Gel nails involve applying multiple coats of a polish-like substance that requires exposure to UV light to dry. Gel nails appear more natural and glossy.
Gel nails are generally more expensive than acrylic nails and look more natural, but they only last up to 14 days. Acrylic nails last longer than gel nails and are harder and more robust, but they also damage the nail bed if not applied correctly with a primer. Gel nails applied without a primer do not usually damage the nail bed.