What Should You Use on Marine Stings?
Saltwater vs Freshwater: What Should You Use on Marine Stings?
One of Marine Medicine’s Great Debates
Let’s wade straight into one of the most practical — and hotly contested — debates in marine medical care:
Do you use hot fresh water or hot salt water? Heat packs or ice packs?
If you’re treating a jellyfish sting in Mallorca, a weever fish wound on a race yacht in Saint-Tropez, or a scorpionfish injury during a charter dive, your choice really matters.
Here’s a breakdown based on current best practice, evidence-based research, and over 25 years of hands-on experience in expedition and marine medicine.
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1. Rinsing the Wound (e.g., Jellyfish Stings)
Do:
Use seawater (salt water)
Do Not:
Never use freshwater — this can trigger massive nematocyst discharge in certain jellyfish, especially Pelagia noctiluca (Mauve Stinger), due to osmotic shock.
Freshwater rinsing causes undischarged stinging cells to fire. This can worsen pain and systemic effects.
Mariottini GL & Pane L. The Mauve Stinger Pelagia noctiluca: biology and venom effects. Toxicon. 2010.
Key Tip: Pre-fill spray bottles with clean seawater and keep them near your swim platform or dive kit.
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2. Applying Heat (e.g., Fish, Urchins, Rays)
Do :
Use hot water immersion at 40–45°C, whether salt or fresh.
• Venom is already in the tissue — water type is less important than temperature.
• Both salt and fresh water denature heat-labile venom proteins.
Thomas C et al. Use of hot water immersion for marine envenomation: a systematic review. Wilderness Environ Med. 2017.
However:
Some divers and crew report that hot freshwater can sting more, possibly due to:
• Tap water additives (e.g. chlorine or softening salts)
• Osmotic discomfort in open wounds
Anecdotally, many Mediterranean crews prefer hot saltwater because it’s gentler, more comfortable, and readily available.
Scientific bottom line: Use what’s practical and safe, but monitor temperature carefully.
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What About Hot Packs?
If you’re mid-charter or offshore and can’t do a full immersion:
Do :
Use a chemical hot pack or heated gel pack
• Apply for 20–45 minutes
• Maintain 40–45°C (use a thermometer if possible)
• Wrap in cloth to avoid burns
Do Not:
Apply cold packs or ice — these may increase pain and delay venom breakdown.
First Aid by Species
Jellyfish (Pelagia)
Do:
Rinse with saltwater, apply hot pack
Do Not:
Freshwater rinse
Vinegar (worsens Pelagia)
Weever, Stingray, Scorpionfish
Do:
Soak in hot water (salt or fresh) at 40–45°C
Do Not:
Ice packs
Cold water
Sea Urchin
Do:
Soak in hot water, remove accessible spines
Do Not:
Dig deeply into tissue
Practical Tips for Yacht Crew
• Keep a thermometer in your medical kit
• Label safe water sources (e.g., kettle-heated seawater, bottled water)
• Stock chemical hot packs in dive bags and grab kits
• Keep seawater spray bottles near water entry points
• Train crew to recognise early systemic symptoms and escalate
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Summary
In my years treating marine stings at sea, the best outcomes came not from perfect conditions, but from calm, confident crews who knew the science and train and review their knowledge regularly, and update risk assessments for each port they visit.
It’s not about fresh or salt — it’s about knowing how heat breaks venom and how osmotic pressure can backfire.
So whether you’re pulling seawater into a bucket on a dive rib or heating bottled water in a galley kettle, it’s the temperature that matters — not the label on the tap.
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Photo Credit: Brad Robertson and the amazing crew at Save the Med Foundation and Bonnie Lass Charters
