Up to 65% of divers report barotrauma to the ears or sinuses at some point in their diving. A head cold is one of the surest routes into that figure. Congestion swells the membranes lining the Eustachian tubes and the ostia, the narrow openings that drain the paranasal sinuses. Once those passages close, the air spaces behind them stop tracking the pressure around you. Pressure then does the work that the swelling started.
DAN's prevention advice for sinus barotrauma and for middle-ear barotrauma opens with the same four words in both places: do not dive congested. Reaching for a decongestant swaps one problem for a worse one. The dose can fade at depth and leave the passages shut on the way up, which is the half of the dive you cannot abort.
What does a blocked nose do to the air spaces?
Boyle's law does the rest. Ambient pressure climbs on descent, the gas in an enclosed space shrinks in proportion, and something has to fill the gap. A sinus that cannot equalise stays near surface pressure and develops a relative vacuum. Capillaries in its lining engorge and burst, and blood fills the cavity until the pressure evens out.
Pain usually eases at that point, and plenty of divers carry on. The middle ear behaves the same way behind a blocked Eustachian tube: negative pressure, swollen tissue, an eardrum bowing inward, then fluid and bleeding. DAN calls middle-ear barotrauma the most common dive injury there is. The guide to equalising your ears covers the descent side, the techniques and the pressure figures behind a ruptured eardrum.
Why is the ascent the part people underestimate?
Venting on the way up is normally passive. Expanding gas finds its own way out of the sinuses and the middle ear, so no technique is needed. Swelling from a cold or from seasonal allergies narrows those same escape routes, and the gas stays where it is.
That is a reverse block. As the diver keeps rising, trapped gas expands against the mucosal lining and the bony walls of the sinus. DAN describes what can follow: a sinus wall bursting into an adjacent sinus that vented correctly, taking the path of least resistance. It reads as sharp facial pain on ascent, then a nosebleed or postnasal drip after surfacing.
A descent can be aborted. An ascent cannot. That asymmetry is the argument against diving congested, and it explains why a clean equalise at 3 metres proves less than it appears to.
Do decongestants make it safe to dive?
They mask the symptom on a timer. Sympathomimetic decongestants such as pseudoephedrine constrict blood vessels in the mucous membranes, which reduces swelling for a few hours. Research cited in the diving literature puts routine use among divers at 6% to 25%, with a further 30% using them occasionally. Popular, and for an obvious reason.
Two problems follow. The first is rebound. DAN Southern Africa's medics put it plainly: once the decongestant wears off, the vessels are no longer constricted and may become more engorged with blood than before. Nasal sprays taken one to two hours before a descent last eight to 12 hours, so a long day can outrun the dose. Repeated use of short-acting over-the-counter sprays can set the stage for a reverse block.
The second problem is the decompression question. A case-control study of 400 divers treated or evaluated at the University of Hawai'i between 1983 and 2010 tested whether decongestant use raises the risk of decompression sickness. The association came out small and not statistically significant: an odds ratio of 1.4, a 95% confidence interval of 0.8 to 2.6, and a P value of .22. Dehydration, repetitive diving and violation of the dive profile all scored higher, at odds ratios of 2.7, 2.8 and 4.9.
The author's caveat carries as much weight as the number. A records-based study may have underestimated the risk, and he called for further research rather than issuing a clean bill. Vasoconstriction increases bubble formation, which is the mechanism behind the concern in the first place. Nothing in those figures licenses a dive that congestion would otherwise rule out.
How do you tell whether your sinuses are clear?
Breathing through your nose proves the nasal passages are open. DAN points out that this says nothing about the paranasal sinuses, which drain through their own narrow ostia. A better check costs nothing. Listen to your own voice, because a blocked sinus changes the resonance and makes you sound stuffy.
- Your voice. Poor nasal airflow is audible. Sounding congested to yourself the night before is a reasonable answer on its own.
- Fullness or pressure. DAN's advice is to skip the dive while there is fullness, pressure or pain across the forehead, the cheeks or behind the eyes.
- Popping and crackling. The same applies to ears that pop or crackle, or that still feel full after a previous dive.
- Yesterday's dive. Blood in the mask, a bloody postnasal drip or dull facial pain after surfacing points at a barotrauma already under way.
- Medication. A training morning is the wrong time to try a drug for the first time. That conversation belongs with a doctor, days in advance.
What about hay fever and allergies?
Allergic swelling closes the same passages a virus does. The medical paperwork treats it seriously. Box A of the Diver Medical Participant Questionnaire lists severe allergies, hay fever and congested airways within the last 12 months, where they limit physical activity. Box C asks about recurrent sinusitis over the same period. A yes to either means a doctor's sign-off before in-water training.
For congestion that is seasonal rather than viral, DAN Southern Africa points at steroid nasal sprays as the safer class. Steroids are not vasoconstrictors, so there is no rebound, and they are intended for longer-term use. The trade-off is timing: about a week of regular use to reach full effect, which solves nothing on a Saturday morning. Suitability, prescription and dose are a doctor's decision.
When can you dive again after a cold?
No day count fits. DAN's fitness-to-dive line after middle-ear barotrauma sets a condition instead of a number. Dive again once swelling and inflammation have resolved and you can equalise adequately. A doctor with an otoscope is the preferred confirmation. Inability to equalise properly is disqualifying, however well you feel otherwise.
Some after-effects outlast the cold. Blood pooled in a sinus can emerge days later as a thick, dark discharge. It makes a serviceable growth medium for bacteria, so a sinus infection is a common sequel. Pneumocephalus and orbital emphysema, air trapped around the brain or behind the eyeball, are rare and serious. Worsening pain, fever, discharge, hearing changes or vertigo all need a doctor.
Pressure changes outside diving count as well. A blocked sinus reacts to a flight home, or to the drive back up to the Highveld, much as it reacts to an ascent. Those changes carry their own timing rules, which the guide to flying after diving sets out.
Sources
- DAN: Sinus Barotrauma, for the ostia, the squeeze and reverse-block mechanisms, the voice check and the complications.
- DAN: Middle-Ear Barotrauma, for the Eustachian tube mechanism, the prevention line and the fitness-to-dive condition.
- DAN Southern Africa: Nasal Decongestants FAQ, for the rebound effect and the steroid-spray comparison.
- Smerz RW, "The Relationship of Decongestant Use and Risk of Decompression Sickness", Hawai'i Journal of Medicine and Public Health, 2014, for the 400-diver case-control figures and the usage rates.
Frequently Asked Questions
Can you dive with a blocked nose if you can still equalise on the surface?
A surface equalise checks the Eustachian tubes at one pressure, on the way down. It says little about the paranasal sinuses and less about the ascent, when venting has to happen without any technique to help it.
What does a reverse block feel like?
Sharp facial pain during the ascent, often followed by a nosebleed or postnasal drip after surfacing. Frontal sinus pain sits above and between the eyebrows and reads like an ice-cream headache. Maxillary pain sits beside the nose and can radiate into the upper molars, because the sinus and the upper jaw share the trigeminal nerve.
Is blood in the mask after a dive serious?
Minor bleeding from the nose or into the throat is typical of sinus barotrauma and seldom severe on its own. DAN cautions divers taking anticoagulants, and notes that telling bloody discharge of sinus origin from discharge of lung origin is beyond someone without medical training. When in doubt, seek medical evaluation immediately.
Are steroid nasal sprays better than decongestants for diving?
DAN Southern Africa considers them the safer option, because steroids do not constrict blood vessels and so produce no rebound. They are slow, needing about a week of use to reach maximum effect. Whether either class suits you is a question for a doctor.
Can you dive with a sinus infection?
An active infection keeps the lining swollen and the ostia narrowed, which is the situation DAN's prevention advice rules out. Sinus infection also appears on DAN's list of complications following a squeeze, since pooled blood feeds bacteria. Treatment and a return date are a doctor's call.
Does a history of sinus trouble affect the course medical form?
Yes. Box C of the Diver Medical Participant Questionnaire asks about sinus surgery in the last six months and recurrent sinusitis in the past 12. Ear disease, ear surgery, hearing loss and balance problems sit in the same box. A yes sends the form to a doctor before any in-water session.
This is general information, not a substitute for a dive medical or advice from a doctor trained in dive medicine. In an emergency, contact your local emergency services and DAN Southern Africa on +27 82 810 6010.
Reviewed September 2026. Devon Ford runs Scuba Evolution, a PADI 5 Star Dive Centre in Glenvista, Johannesburg.
