Complex sentence: The drawback of using chlorine in swimming pools is that the chlorine reacts with the proteins in human hair and skin (see Hypochlorous acid), and becomes chemically bonded.
Split into simpler sentences: The drawback of using chlorine in swimming pools is that the chlorine reacts with the proteins in human hair and skin (see Hypochlorous acid). Once the chlorine reacts with the hair and skin, it becomes chemically bonded.