In the “Sea Lice Season” article from our April issue,
we recommended divers feeling the burn of sea lice should
immediately apply a mix of alcohol and vinegar, followed by
hydrocortisone cream, to reduce the pain. Subscriber and
emergency physician Ted Shieh, M.D. (Chicago, IL) wrote in
to say medical experts have changed these recommendations
and the consensus now is immediate water immersion.
“Treatment of exposure to thimble jellyfish larvae is
  the same as stings from jellyfish, fire corals, sea urchins,
  anemones and fish -- soak or rinse the affected areas in a
  warm-water bath or shower with the temperature as hot as
  tolerable, usually 112 to 120 degrees Fahrenheit,” says Shieh.
  “The treatment should continue until painful symptoms
  subside, up to 90 minutes, although 10 minutes of a warm
  shower or soak is adequate for most stings. Having been
  stung by numerous sea jellies and sea lice, I can attest to the
  effectiveness of a hot shower.”
The rationale: Because most marine animals’ toxins can
  be destroyed by heat, hot water can destroy the venom both
  inside and outside the skin. “Vinegar can only neutralize
  stings that didn’t penetrate the skin, but it can be used only
  if it’s immediately available and prior to a hot-water dousing.
  Just in case hot water is not available after a dive, consider
  packing a heating pad, the squeeze-and-shake kind, to put
  over the exposed area.”
As for treating allergic skin reactions, Shieh recommends
  a non-sedating antihistamine like Zyrtec or Claritin (loratadine),
  and a steroid cream such as hydrocortisone. “And of
  course, I certainly agree that when stings go beyond mild to
  moderate symptoms, it’s time to call a physician -- or invite
  one on your next dive trip.”