Why is is healthful to perspire?

Your question makes no sense: 'Why is is healthful to perspire?' the 'is' is repeated twice and healthful is not a word. To be honest I have no idea what you are asking. People sweat to cool them down when they are too hot. They also do it when they are afraid because of adrenaline and maybe also to make them slippery for attackers? That is just my idea. Why do you say things that are pointless and confusing like 'I am not my sister'? It is physically impossible to be your own sister. What is the question here and why did you say so much stuff?