How to Stop Feeling Sick After Swimming

Feeling sick after swimming, whether that means nausea, dizziness, headache, or a vague sense of being unwell, usually traces to one of a handful of identifiable causes. Cold water entering the ear canal, chemical irritants in treated pools, blood sugar drops, and even the simple act of standing up after being horizontal in water can all trigger post-swim malaise. The good news is that once you know which trigger is behind your symptoms, most of them are preventable with straightforward adjustments to how you prepare, swim, and recover.

Why Cold Water in Your Ears Makes You Dizzy

One of the most common and disorienting sensations after swimming is a sudden spell of vertigo, that feeling that the room is spinning or that you might topple over. If it hits right after you surface or step out of the water, the culprit is often cold water that entered your ear canal. When cold water reaches the inner part of the ear, it can trigger reflex activity in the semicircular canals, the fluid-filled loops deep inside your ear that help you maintain your sense of balance.¹ This is called caloric vertigo, and it can range from a mild wobble to full-blown nausea. The temperature difference between the water and your body essentially confuses your balance sensors, sending signals to your brain that conflict with what your eyes and muscles are reporting.

The effect is worse when there is a big temperature gap, such as jumping into an unheated outdoor pool or cold lake. It also tends to be worse on one side if one ear lets in more water than the other, since uneven stimulation of the two labyrinths creates a stronger mismatch signal. People who swim regularly in cold water sometimes build up bony growths in the ear canal called exostoses, which can trap water and make the problem chronic. But even without that complication, a single cold-water swim can leave you feeling queasy for minutes afterward.

A related issue is neck-position vertigo. In at least one documented case, a swimmer experienced repeated bouts of room-spinning dizziness specifically while doing freestyle, traced to the repetitive head-turning motion irritating structures in the cervical spine.² If your dizziness reliably appears during one stroke style but not others, consider whether the neck rotation pattern is contributing.

Earplugs Actually Help, but Not All Equally

If cold water entering the ears is your primary trigger, earplugs are the most direct fix. However, not all earplugs perform the same in the water. A controlled study testing several commercial earplug types found that water still got in during surface swimming in nearly half of ears tested, and the rate climbed to almost 90 percent during vertical submersion. The soft silicone putty-style plugs performed best across all swimming positions, with significantly lower rates of water penetration than foam or flanged designs.³ The takeaway is that moldable silicone plugs that conform to your outer ear are worth the small extra cost over generic foam plugs, which tend to let water seep past.

Custom-molded earplugs from an audiologist offer the best seal, and they are worth considering if you swim frequently and vertigo is a recurring problem. A neoprene headband worn over the ears can add another layer of protection by holding plugs in place and reducing the flow of water around them.

Chemical Irritation in Indoor and Treated Pools

That queasy, headachy feeling you get at indoor pools may not be in your head. Chlorine itself is not usually the villain; the problem is what chlorine creates when it reacts with organic material brought in by swimmers, things like sweat, skin oils, urine, and cosmetics. These reactions produce compounds called chloramines and other disinfection byproducts, and they concentrate in the air just above the water surface, exactly where you are breathing.

Investigations into outbreaks of illness at two indoor hotel pools found that a total of 72 people developed eye and respiratory symptoms including burning eyes, tearing, and cough within minutes of entering the pool area. Symptoms worsened with longer exposure time and were sometimes prolonged and severe.⁴ A separate investigation at an indoor waterpark found that employees reported eye irritation, nose irritation, difficulty breathing, coughing, and even vomiting, all consistent with ongoing exposure to disinfection byproducts.⁵

Indoor facilities are more problematic than outdoor ones because the byproducts accumulate in enclosed airspaces. Poorly ventilated indoor pools are the worst offenders. If you consistently feel nauseated, headachy, or short of breath at a particular indoor pool, the ventilation system may be inadequate. Switching to an outdoor pool or a facility with better air handling can make a dramatic difference. Showering thoroughly before you get in the water also helps at a population level, since the fewer organic compounds swimmers introduce, the fewer irritating byproducts the chlorine produces.

Blood Sugar Drops and Dehydration

Swimming burns through energy faster than most people realize, partly because the body is simultaneously working to maintain its core temperature in water that is almost always cooler than body temperature. If you swim on an empty stomach or after a long gap since your last meal, blood sugar can fall low enough to cause nausea, lightheadedness, and that shaky, washed-out feeling.

Research on endurance athletes showed that maintaining blood glucose levels during sustained exercise made a major difference in how long they could keep going. Swimmers who consumed a slow-releasing carbohydrate before exercise maintained higher plasma glucose during pre-swimming efforts and lasted roughly 70 percent longer before reaching fatigue compared to those who drank plain water.⁶ You do not need a specialized sports supplement to get this benefit. A banana, a piece of toast with peanut butter, or a small handful of dried fruit eaten 30 to 60 minutes before swimming gives your body accessible fuel.

Dehydration is the other half of the equation, and it is sneaky in the pool because you do not feel yourself sweating. You absolutely do sweat while swimming; you just cannot tell because the water washes it away. Mild dehydration on its own causes headaches, nausea, and fatigue. Drinking water before and after your swim, and keeping a water bottle at the pool deck for sips during breaks, is one of the simplest interventions with the biggest payoff.

The Problem of Drinking Too Much Water

On the opposite end, some swimmers, especially those doing long open-water sessions, can overcorrect and drink so much water that their blood sodium drops dangerously low. This condition, called exercise-associated hyponatremia, is defined by a fall in blood sodium below 135 mmol/L during or up to 24 hours after prolonged physical activity. It has been reported across nearly every form of endurance exercise and is driven primarily by excessive water intake.⁷

Mild hyponatremia causes nausea, headache, confusion, and bloating, symptoms that overlap with many other post-swim complaints and can easily be mistaken for something else. Severe cases can be life-threatening. The practical lesson is to drink to thirst rather than forcing yourself to consume a predetermined amount of water during extended sessions. If you are swimming for over an hour, an electrolyte drink is a better choice than plain water because it helps maintain sodium balance.

Dizziness When You Stand Up After Swimming

Here is one that catches people off guard. You feel fine in the water, fine on the wall, and then the moment you climb the ladder or stand up on the pool deck, your head spins and your stomach lurches. This is orthostatic hypotension, a temporary drop in blood pressure that happens when you shift from horizontal to vertical. Swimming makes it worse than, say, getting up from lying on a couch because water pressure on your body helps push blood back toward your heart. The moment you leave the water, that external support disappears, blood pools in your legs, and your blood pressure drops.

Research on people prone to orthostatic dizziness found that simple physical maneuvers can make a meaningful difference. Crossing the legs while standing increased mean blood pressure enough to prevent dizziness in patients who otherwise became dizzy within 10 minutes of standing. Squatting produced an even larger blood pressure increase.⁸ You can use this after swimming: when you get out of the pool, pause at the edge. Sit on the deck for a moment before standing. If you feel the dizziness starting, cross your legs or squat briefly. It takes only a few seconds and can prevent the wave of nausea that comes with a blood-pressure drop.

This effect is more pronounced after long swims, in warm pool environments where blood vessels are already dilated, and in people who are dehydrated. Older adults and anyone taking blood pressure medication are more susceptible, so the sit-before-you-stand advice is especially relevant for those groups.

Sinus Pressure and Post-Swim Headaches

Headaches after swimming are frequently linked to sinus pressure. Water can enter the nasal passages and sinuses, especially during flip turns, diving, or swimming without nose clips. The sinuses are air-filled pockets that normally equalize pressure on their own, but when water gets in or swelling from irritation blocks the drainage pathways, the result is a building pressure headache that may not peak until an hour or more after you leave the water.

Cold water adds another dimension. A cold stimulus headache, essentially an ice-cream headache triggered by cold water contact with the face or forehead, is a recognized phenomenon among swimmers and divers.⁹ It is usually sharp and short-lived, but it can leave a residual dull ache. People with a history of migraines are more prone to cold-triggered headaches in the water.

Prevention strategies include wearing a nose clip if sinus flooding is the issue, or a neoprene cap that covers the forehead if cold stimulus headaches are the pattern. Decongestant nasal spray before swimming can help keep sinus passages open, though it should not become a daily habit due to rebound congestion. If your headaches consistently appear after swimming in a specific pool but not others, circle back to the chloramine issue discussed earlier, since chemical irritation of the nasal lining can mimic sinusitis symptoms.

Open Water and Blue-Green Algae

Swimming in lakes, reservoirs, or slow-moving rivers introduces a different set of risks. One of the most underappreciated is cyanobacteria, commonly called blue-green algae, which thrive in warm, nutrient-rich freshwater. During blooms, these organisms release toxins that can cause nausea, vomiting, diarrhea, skin rashes, and respiratory irritation.

A study of over 850 recreational water users found that people who had contact with water containing higher concentrations of cyanobacteria cells reported significantly more symptoms at the seven-day follow-up. The risk increased with both the duration of exposure and the concentration of cells in the water. People exposed to more than 5,000 cells per milliliter for over an hour had a notably higher symptom rate than those who stayed out of the water entirely.¹⁰

Blooms often look like green or turquoise scum on the water surface, but they can also be invisible at lower concentrations. Many local health departments issue advisories when cell counts reach dangerous levels, so checking before you swim in natural bodies of water during warm months is a reasonable precaution. If you do swim in water that turns out to have a bloom, shower as soon as possible and avoid swallowing any water. Symptoms from mild exposure typically resolve on their own within a few days, but persistent vomiting or difficulty breathing warrants medical attention.

When It Might Be Something More Serious

Most post-swim sickness is uncomfortable but harmless. Occasionally, though, the symptoms signal something that needs medical evaluation. Swimming-induced pulmonary edema is a condition where fluid accumulates in the lungs during or shortly after swimming, without the person having inhaled water. It produces acute shortness of breath and sometimes a cough that brings up blood-tinged sputum.¹¹ The underlying problem is that immersion in water shifts blood toward the central circulation, increasing pressure in the pulmonary capillaries to the point where fluid leaks into the air spaces of the lungs.¹²

This is rare in casual pool swimmers but shows up more often in triathletes, military combat swimmers, and people doing intense open-water efforts in cold conditions. Cold water makes it worse because it constricts blood vessels, amplifying the pressure increase. If you develop a persistent cough, frothy or pink-tinged sputum, or feel severely short of breath after swimming, get out of the water and seek medical help. Unlike garden-variety post-swim malaise, this condition can deteriorate quickly if ignored.

A Practical Pre- and Post-Swim Routine

Putting all of this together, here is what a prevention-oriented swim routine looks like:

• Before you get in: Eat a light snack 30 to 60 minutes beforehand. Hydrate with water or an electrolyte drink. Shower to rinse off oils, lotions, and sweat so you contribute fewer byproducts to the pool chemistry.
• Gear choices: Moldable silicone earplugs if you are prone to dizziness. A nose clip if sinus pressure or headaches are your pattern. Goggles for every session, since chemical irritation to the eyes compounds the overall feeling of being unwell.
• During the swim: Drink to thirst, not on a rigid schedule. If you are in the pool for under 45 minutes, plain water is fine. For longer sessions, include some sodium and carbohydrate.
• Getting out: Sit at the pool edge before standing. Let your cardiovascular system readjust to gravity. If dizziness hits, cross your legs or squat briefly.
• After: Rinse your ears by tilting your head side to side and gently pulling the earlobe to drain trapped water. Shower to wash off chloramines from your skin and hair. Eat something within 30 minutes to replenish glycogen stores.

The specific combination of steps that matters most depends on which symptoms you experience. Someone whose primary complaint is nausea benefits most from the eating and hydration advice. Someone who gets dizzy needs the ear protection and the exit strategy. Someone who leaves the pool with burning eyes and a scratchy throat might need a different pool entirely, one with better ventilation or outdoor air. Tracking which symptoms show up and under what conditions, type of pool, water temperature, how much you ate beforehand, how long you swam, is the fastest way to narrow down your personal triggers and stop the cycle of feeling awful every time you get out of the water.

Why Some People Are More Affected Than Others

There is a real individual variability to post-swim sickness that goes beyond just preparation. People with a history of motion sickness tend to be more susceptible to the vestibular disruption from cold water in the ears. Those with asthma or pre-existing airway sensitivity react more strongly to chloramines. Anyone with low blood pressure at baseline, whether from medication, fitness level, or just genetics, is more likely to get that orthostatic crash when climbing out.

Age plays a role too. Children tend to swallow more pool water, exposing them to more disinfection byproducts and more stomach upset from ingesting chlorinated water. Older adults are more vulnerable to blood pressure swings and dehydration. Competitive swimmers who train daily may develop chronic low-grade chemical sensitivity that recreational swimmers never encounter, simply because cumulative exposure adds up.

If you have tried the basics, eating beforehand, staying hydrated, wearing earplugs, choosing well-ventilated pools, and still feel consistently sick after swimming, it is worth mentioning to your doctor. Chronic post-swim symptoms occasionally point to something like exercise-induced bronchoconstriction, eustachian tube dysfunction (ear disorders since learning to swim or dive are remarkably common, reported by nearly 80 percent of respondents in one survey of divers⁹), or an underlying cardiac issue that only manifests under the unique hemodynamic stress of immersion. These are not common explanations, but they are treatable ones, and ruling them out can give you confidence that your post-swim sickness is manageable with the simpler strategies.