Royal Navy researchers at the Institute of Naval Medicine have tested whether acidic drinks such as orange juice or Coca-Cola could be used to rinse the mouth after a rebreather “caustic cocktail”. In the laboratory, acidic liquids lowered the pH of a caustic solution far more than neutral liquids, and produced no heat. Anyone who looks after divers, from a diver medic on a vessel to a paramedic at the quayside, should know what this study found and what it cannot yet tell you.
Why this matters
A closed-circuit rebreather (CCR) recycles the diver’s exhaled gas. Carbon dioxide is removed by a canister of soda lime, a sodium hydroxide-based absorbent. If water gets into the breathing loop it reacts with the absorbent to form a strongly alkaline liquid, the “caustic cocktail”. A Divers Alert Network (DAN) survey paper describes it as concentrated caustic soda with a pH between 12 and 14.
Swallowed or inhaled, it burns. Effects range from coughing, breathlessness and difficulty swallowing to severe internal corrosive injury. A DAN case report describes a diver who inhaled it at 10 metres, could not speak for about 30 minutes after surfacing, and had a burning throat for days.
The accepted first aid is to remove the mouthpiece and flush the mouth repeatedly with water, ideally fresh. Seawater is acceptable if that is all there is. Alongside this sits a long-standing rule: never rinse with anything acidic. The fear is an exothermic reaction, meaning neutralising an alkali with an acid releases heat and could worsen the burn.
That rule has not always been the advice. The DAN survey authors note that a vinegar and water mixture was recommended in the 1970s. Nor do all divers follow it. Of 413 certified CCR divers surveyed, 237 (57%) had experienced at least one event. For their most recent event, 186 (79%) rinsed with water, 19 (8%) used a fizzy drink, 5 (2%) fruit juice and 5 (2%) a mild acid. One diver reported mouth burns after gargling with a fizzy drink. The Royal Navy team’s point was that the “never use acid” rule rests on very little published evidence.
What the researchers did
Adam Lee, Catherine Moore and Adam Griffiths of the Underwater Medicine Department, Institute of Naval Medicine, Portsmouth, published the study in Diving and Hyperbaric Medicine on 31 March 2026 (volume 56, issue 1, pages 83 to 87).
This was an in vitro study, meaning it was done on the bench and not in people. The team modelled an ingested caustic cocktail using a sodium hydroxide solution. They added different diluents, meaning liquids that might be used to rinse or dilute the caustic: acidic options, orange juice and Coca-Cola, and neutral options. They measured the change in pH and temperature.
The full paper is under a 12-month embargo and only the abstract is freely available. The concentration of the caustic solution, the volumes used and the number of repeat runs are not in the abstract, so they are not reported here. The journal’s editor, Professor Simon Mitchell, called it a simple experiment.
What they found
Acidic diluents reduced pH significantly more than neutral diluents: a mean fall of 5.99 compared with 0.78 (P = 0.015). The pH scale is logarithmic, so a fall of almost six units is a very large change in alkalinity.
On safety, there was no statistically significant difference in temperature change between the two groups (P = 0.32), and no exothermia was generated. The heat that the traditional rule warns against did not appear in this model.
The authors propose that orange juice or Coca-Cola may be more effective irrigation solutions than fresh or seawater, and that advice to CCR divers could change.
Strengths and limitations
The study tests a safety claim repeated for decades with little evidence behind it. It measured the exact thing the rule warns about, heat, and found none. It comes from a military diving medicine unit that supports rebreather divers, so the question is a practical one.
The limitations are substantial. A beaker is not a mouth or an airway. Alkali injury depends on contact time, concentration and depth of penetration, none of which a bench model shows. The study modelled ingestion, not inhalation, and says nothing about an acidic, sugary liquid reaching the lungs. Acidic drinks may also irritate burned mucosa. There were no patients and no outcomes.
Only the abstract is public, so the methods cannot be checked in full. The journal’s contents page lists the paper under review articles while the editor describes an experiment, so even the study type is unclear. The DAN survey is self-reported and cannot show cause and effect.
The Royal Navy and technical divers use rebreathers. Most commercial offshore divers use surface-supplied equipment, so an offshore medic is less likely to see a caustic cocktail than a diver medic working with a CCR team.
What it means for your practice
Do not change what you do or teach on the basis of one laboratory study. The accepted first aid stands: mouthpiece out, flush the mouth repeatedly with water, fresh if possible, seawater if not, and get the diver out of the water. Local protocols and national guidance such as JRCALC govern your practice.
- Diver medics and offshore medics: ask about caustic cocktail in any CCR diver with a sudden cough, burning mouth or hoarse voice. Treat it as an alkaline injury of the mouth and upper airway. Watch for swelling, stridor and aspiration, and seek diving medical advice early. Do not start recommending fizzy drinks or juice.
- Paramedics: record the time of exposure and what was used to rinse. Reassess the airway and manage as a chemical burn under your service’s guidance. Hand over the rebreather history.
- First responders: remove the diver from the source, rinse the mouth with water and call for help.
- Everyone: if a diver has already rinsed with juice or a fizzy drink, note it. This study suggests heat is unlikely; it does not show acidic rinses are safe in people.
Watch for the full paper when the embargo lifts, and for any change in guidance from diving medical bodies.
Reflect
- How would you recognise and manage a diver with a suspected caustic cocktail, and when would you escalate?
- Why does a bench result not transfer directly to a patient, and what else would you want to see before changing a rinse protocol?
- In your setting, where would you get fresh water quickly, and who would you contact for diving medical advice?
- If a colleague told you that Coke is now the recommended rinse for caustic cocktail, how would you respond?
Read the original
- Diving and Hyperbaric Medicine: Efficacy and safety of potential irrigation diluents following ‘caustic cocktail’ ingestion (Lee, Moore and Griffiths), 2026 (abstract)
- PubMed record: Efficacy and safety of potential irrigation diluents following ‘caustic cocktail’ ingestion, 2026
- Diving and Hyperbaric Medicine volume 56 issue 1, including the editor’s comment on the study, March 2026
- Diving and Hyperbaric Medicine: A survey of caustic cocktail events in rebreather divers (Buzzacott and colleagues), 2022
- Divers Alert Network: Caustic cocktail rebreather survey, research study page, 2022
- Divers Alert Network: A case of caustic cocktail, case summary, 2023
Published 25 October 2026. Last reviewed October 2026.
These summaries are for education and CPD only. They are not clinical guidelines. Always practise within your scope of practice and follow your employer’s protocols and national guidance such as JRCALC and Resuscitation Council UK.