The boggart is a ghost-like creature that usually resides in dark, closed spaces such as a wardrobe or a drawer. No one knows what a boggart's true form is because every time a person tries to look, the boggart shape-shifts into the thing that the person's worst fear is. Its lifespan is indefinite. However, if a boggart turns into a magical creature such as a dementor, its magic will be weakened. So if the boggart/dementor approaches you and gives you the Kiss, it probably will not have the full effect has a real Kiss would. When facing a boggart, it would be better to have someone accompany you in order to confuse it and give you more time to kill it. 

           There is only one way to completely finish off a boggart, and that is laughter. However, in order to disable it so you are not so scared out of your wits that you are unable to laugh, there is a spell. If you visualize something funny, point your wand directly at the boggart and shout, Riddikulus!, that thing that you just thought of will appear on the boggart, which will confuse it. It will also give you more motivation to laugh. For example, when Ron Weasley was facing a giant hairy spider, he gave it roller skates, so that it slid and tripped over its legs and encouraged him to laugh.