How dangerious are Portuguese man of war to humans?

Their powerful stings are extremely painful to humans, but is not fatal. If you get stung, grab a towel to remove the stingers and put hot or very cold water on it. Do not pour vinegar or urinate on it because it would make the sting more painful. If you see dead portuguese man of wars on land, do not touch them or step on them since they can still give you a sting. Do not walk underneath their heads because you may accidently reach their poisonous tentacles and get stung. Instead walk around it.