Asthma was treated as an absolute disqualifier for diving until roughly 2002. Current consensus from the South Pacific Underwater Medicine Society, the UK Sport Diving Medical Committee, and DAN is that some asthmatics can safely dive after proper evaluation. The decision is not yours to make on a form — it belongs to a dive-trained physician who can assess your specific type, severity, control, and lung function. The RSTC form will route any yes-answer on asthma straight to that physician. Tick yes, get the assessment, find out what your specific situation allows.
Why asthma is medically relevant for diving
Two physiological concerns are doing the work here.
Pulmonary barotrauma on ascent. Your lungs hold compressed gas at depth. On the way up, that gas expands. Normally you exhale and it leaves through your airways without issue. If part of your airway is constricted — a bronchospasm, for example — the gas behind the constriction can’t escape fast enough. The local pressure rises, alveoli rupture, and gas can enter the bloodstream as an arterial gas embolism. AGE is fatal in minutes if it reaches the brain.
This is the same mechanism that makes “never hold your breath” the most-repeated rule in dive training. The worry with asthma is that a bronchospasm can produce the same effect involuntarily.
Bronchospasm triggered by the dive environment itself. Scuba breathing is cold, dry, dense compressed air through a regulator. Several of the things asthmatics react to are present:
- Cold air (cold-induced asthma)
- Dry air (compressed air from a tank is essentially zero humidity)
- Exertion (currents, kicking with gear)
- Sometimes salt mist on the surface
- Occasionally an allergic trigger if the tank fill room had contaminants
A diver with cold- or exercise-induced asthma may have controlled symptoms on land and a clean spirometry test, then bronchospasm in the water.
What changed in the consensus
In the 1980s and 1990s, every major recreational agency treated asthma as an automatic no. The reasoning was conservative: any chance of bronchospasm at depth was too much.
The picture shifted through the late 1990s and early 2000s as several studies and consensus statements were published:
- Edmonds, Lowry, Pennefather and Walker — the standard text on diving medicine — softened the position across editions.
- DAN’s Asthma and Diving consensus workshop in 1995, refined through the 2000s, separated asthma into subtypes and proposed individual evaluation rather than blanket exclusion.
- The South Pacific Underwater Medicine Society issued guidance accepting that mild, stable, well-controlled asthma without cold- or exercise-triggered symptoms should not be an automatic exclusion.
- The UK Sport Diving Medical Committee adopted similar guidance via the UK Diving Medical Reference Group.
The 2020 revision of the RSTC questionnaire reflects this. Asthma now triggers a dive doctor referral, not an automatic disqualification.
The current scientific picture is roughly: the absolute risk of pulmonary barotrauma in a well-controlled asthmatic with normal spirometry appears to be only modestly higher than in a non-asthmatic, and the population of asthmatics now diving without incident has grown large enough to support this empirically. That said, “modestly higher” is not zero, and the dive-doctor evaluation is the mechanism that filters out the people for whom the risk is genuinely elevated.
What a dive-trained physician typically evaluates
The evaluation is more thorough than a regular asthma check-up. The standard considerations a dive doctor will work through:
Type of asthma. Allergic, exercise-induced, cold-induced, occupational, mixed. Cold- and exercise-induced asthma raises specific dive concerns because of the trigger overlap with the dive environment.
Frequency and severity of symptoms. Daily symptoms, weekly, monthly, or only with specific exposures. Recent hospitalisations or emergency rescue inhaler use. The general considerations for clearance lean heavily on long stretches without symptoms.
Medication regimen. Inhaled corticosteroids for prevention versus rescue inhaler use, frequency of each, escalation history.
Spirometry / lung function test. A formal pulmonary function test, often including a bronchodilator response and sometimes a bronchial challenge with methacholine. The physician is looking at FEV1, FEV1/FVC ratio, and how reactive the airways are.
Exercise tolerance. Can you sustain moderate aerobic exertion (climbing stairs, running, swimming) without symptoms or rescue inhaler use? This roughly maps to the demands of recreational diving.
Recent control. How long since the last symptomatic episode. Twelve to twenty-four months without symptoms is a common reference point in published guidance, though individual evaluation overrides any universal threshold.
Who typically gets cleared
Based on published guidance from DAN, SPUMS, and UKDMC — these are general considerations, not promises:
- Stable, well-controlled asthma with normal spirometry and no symptoms in the previous 12–24 months
- Asthma controlled on a preventer inhaler with no rescue inhaler use during exertion
- Allergic asthma with known, avoidable triggers that don’t include cold air or exertion
- Childhood asthma that resolved and hasn’t recurred in adulthood
Who typically isn’t cleared
Again, general considerations only — the dive doctor decides on your specific case:
- Active symptomatic asthma with regular rescue inhaler use
- Exercise-induced asthma triggered by moderate exertion
- Cold-induced asthma triggered by cold air exposure
- Recent hospitalisation or ER visit for an asthma exacerbation
- Steroid-dependent asthma requiring oral corticosteroids
- Severe atopic asthma with frequent flares
- Spirometry showing significant obstruction even on medication
If a physician declines you for diving but your asthma improves later, you can be re-evaluated. The decision is not permanent for most people.
Practical steps before booking
Get evaluated before you book. This applies generally to anything on the RSTC form but doubly so for asthma. The evaluation usually involves spirometry, which most general practitioners can order but a dive-trained physician will interpret with diving-specific criteria. Both visits take time to arrange.
The Divers Alert Network maintains referral directories:
- DAN Europe at daneurope.org
- DAN World at diversalertnetwork.org
- UKDMC at ukdmc.org for UK-based divers
- DAN AP at danap.org for Asia-Pacific
Bring your spirometry results and inhaler prescriptions to the dive medical. The physician will want to see actual numbers, not your description of your asthma.
Be honest with the dive shop. If you’re cleared, bring the signed paperwork. Tell the instructor about your asthma even with clearance, what your triggers are, and what your rescue plan looks like. Good shops will adjust briefing pace, signal arrangements, and buddy assignments accordingly.
Inhalers underwater — what the practice actually is
This part comes up a lot and is worth separating into surface use and underwater use.
Surface use. Many cleared asthmatic divers carry their rescue inhaler in the dry bag on the boat. If symptoms surface between dives, the inhaler is there. This is a reasonable precaution and most operators are comfortable with it.
Underwater use. Using a rescue inhaler underwater is not standard practice. The inhaler is not designed for use at depth, the propellant behaves unpredictably under pressure, and if you’re symptomatic enough underwater to need rescue medication, the standard response is to abort the dive, signal your buddy, and ascend slowly with controlled breathing — not to fish around in a BCD pocket for an inhaler at 18 metres.
The implication: if you genuinely think you might need rescue medication during a dive, you’re not in the cleared-for-diving group. The clearance criteria are specifically set so that ordinary recreational dive conditions don’t trigger your asthma. If they do trigger it, the situation has changed and you need re-evaluation.
A quick reference
| Situation | Typical handling |
|---|---|
| Childhood asthma, no symptoms in 10+ years | Dive doctor often clears with normal spirometry |
| Mild allergic asthma, controlled, no exertion symptoms | Dive doctor often clears after assessment |
| Asthma controlled on daily inhaled steroid, no rescue use | Often cleared, individual evaluation |
| Asthma with occasional rescue inhaler use during exertion | Frequently declined or deferred until control improves |
| Cold-induced asthma | Frequently declined for cold-water diving |
| Exercise-induced asthma | Usually declined |
| Recent hospitalisation for asthma | Usually declined until stable for 12+ months |
| Steroid-dependent (oral steroids) asthma | Usually declined |
This is orientation, not your answer. A dive-trained physician applies these criteria to your specific lung function and history.
What to do if you’re declined
Asthma control improves over time for many people. If you’re declined now, the path forward is:
- Work with a respirologist on long-term control, not just symptom suppression.
- Track your symptom-free intervals. The relevant question for re-evaluation is usually 12–24 months without symptoms.
- Maintain regular spirometry so you have a longitudinal record.
- Re-apply for a dive medical evaluation when your control has been stable for the relevant period.
Many divers who were declined in their 20s or 30s come back a decade later with controlled asthma and get cleared.
A note on warm-water versus cold-water diving
Some dive doctors apply slightly different thresholds for warm-water recreational diving in tropical destinations (Egypt, Thailand, Indonesia) versus cold-water diving in temperate seas (UK, Norway, Pacific Northwest). The cold-air trigger is a meaningfully larger factor in cold-water diving. Discuss your travel plans with the physician — if you’re cleared for Thailand but planning a UK trip later, that conversation is worth having explicitly.
Ready to book?
We compare Koh Tao dive shops on instructor experience, group size, and how they handle medical clearances. Once you have your dive-doctor clearance in hand, you can pick the shop that fits.