As the Portuguese man o'war is not a true jellyfish (it's a colony of individual siphonophores), the sting is NOT a sting -- the lesions and irritation extend along the whip-like range of contact and continue to damage subdermal tissue. Rinsing with heated water should continue when one leaves the water, and application of vinegar or dilute ammonia to destroy the nematocysts (stinging cells) in the wounds. Some people may not respond as well to the use of vinegar.Clinging cells can also be carefully removed with shaving cream and a blade razor, followed by application of hydrocortisone to reduce the immune system reaction to the injury.