Manufactured chlorine contains chemical additives to increase its effectiveness and shelf life. It s  these additives which cause your eyes to turn red, makes your skin sticky, and makes your hair feel brittle. This type of chlorine has to be added to the pool constantly because it evaporates with the water, and it is diluted with rain or when fresh water is added to the pool. Salt water chlorination generates natural chlorine on site by converting salt into free chlorine. More details on how this is  done are below.