They are not cosmetics or over-the-counter merchandise. They are medical devices regulated by the U.S. Food and Drug Administration. Places that advertise them as cosmetics or sell them over-the-counter, without a prescription, are breaking the law.
They are not “one size fits all.” An eye doctor (ophthalmologist or optometrist) must measure each eye to properly fit the lenses and evaluate how your eye responds to contact lens wear. A poor fit can cause serious eye damage, including:
scratches on the cornea (the clear dome of tissue over the iris—the part of the eye that gives you your eye color)
corneal infection (an ulcer or sore on the cornea)
conjunctivitis (pink eye)
decreased vision
blindness