A breaking wave does more than rearrange water. It traps air, breaks that air into bubbles and sends some of their contents back into the atmosphere. The visible mist above rough surf is only the largest part of the exchange. Much smaller droplets can remain suspended, shrink as water evaporates and travel inland on the wind.
These sea-spray aerosols are not sterile grains of salt. Depending on the place and season, they can carry organic molecules, fragments of algae, viruses, bacteria and pieces of bacterial cell walls. People near a coast therefore do not merely smell the ocean. They inhale a faint and changing sample of its surface biology.
That observation has encouraged an intriguing explanation for the often reported association between coastal living and better health. Perhaps the sea affects people not only through exercise, cleaner views, cooler air or psychological restoration, but also through direct contact with airborne marine compounds.
Laboratory studies now show that the idea is biologically plausible. Sea spray collected beside the North Sea activated sensors used by the human innate immune system, while a later experiment found that seasonally collected spray changed gene activity in human bronchial cells. But plausible is not proven. Neither experiment showed that breathing at the beach prevents disease, improves immunity or explains why some coastal populations report better health.
How the ocean enters the air
When waves break, air is forced beneath the surface. The resulting bubbles rise and collect material along the way. At the surface, a bubble’s thin cap can rupture into tiny film droplets, while the collapsing cavity can fire a narrow jet upward and produce somewhat larger droplets.
Some droplets fall back almost immediately. Others are small enough to remain airborne. As their water evaporates, the remaining particles become more concentrated packages of sea salt and whatever biological or organic material was swept into them.
Researchers recreate this process with devices such as a Marine Aerosol Reference Tank, or MART. Water circulates through the apparatus, a plunging jet produces bubbles, and the bubbles burst under controlled conditions. Such systems cannot reproduce an entire coast, but they let scientists make repeatable aerosol samples while reducing contamination from soil, traffic and other land-based sources.
Earlier laboratory work on bringing breaking waves into controlled tanks showed why this matters. A particle’s size and chemical mixture depend on bubble physics and the biology of the source water. “Sea spray” is therefore a category, not a uniform substance.
A droplet carries more than salt
The ocean surface is a chemically busy boundary. Oils, proteins, carbohydrates and microbial material accumulate at or near it. Rising bubbles can scavenge some of that material, which means the aerosol leaving the surface does not necessarily have the same composition as a random cup of seawater.
Bacteria can enter the air intact, but immune cells do not need to encounter a living bacterium to respond. Gram-negative bacteria possess lipopolysaccharide in their outer membranes. Part of that molecule is commonly described as endotoxin, and immune receptors can recognize it even when the original cell is no longer viable.
This is not automatically beneficial or harmful. The innate immune system is the body’s rapid, general-purpose surveillance layer. It recognizes common molecular patterns and coordinates a response before the slower, highly specific adaptive immune system has fully mobilized.
A mild signal may be handled without consequence or may help regulate later responses. A strong or prolonged signal can contribute to inflammation. The result depends on dose, chemical context, route of exposure and the condition of the exposed tissue. “Immune activation” is a measurement, not a synonym for “immune improvement.”
What the 2024 cell experiment found
For a study published in Science of the Total Environment, researchers collected aerosols at Ostend, Belgium, during eight sampling days from 20 March to 13 April 2023. On one day each week they collected spray in the field. On another, they used seawater in a MART to generate aerosol under more controlled conditions.
The 2024 study characterized 18 field samples and 18 tank-generated samples for sodium, total bacterial counts and endotoxin. Field air contained between 3,000 and 600,000 bacterial cells per cubic metre, averaging about 200,000. Measured endotoxin ranged from 7 to 1,217 endotoxin units per cubic metre.
The laboratory-generated aerosol generally carried more bacterial material. That was useful for creating a wide range of concentrations, although it is also one reason the tank exposures should not be treated as a literal copy of an ordinary walk along the coast.
The team exposed engineered human reporter cell lines to aerosol extracts for about 24 hours. Two lines were designed to report activation of Toll-like receptor 4 and the TLR2/6 receptor pair. A third, derived from human monocytes, reported activity in NF-κB and interferon regulatory factors, or IRFs.
Nearly every tested field and tank sample produced activation above the negative controls. Across the samples, activity in all four readouts increased with bacterial counts, endotoxin concentrations or both. The simple correlations were statistically strong, with all reported probability values below 0.001 and coefficients of determination of at least 0.55.
Four signals, not a health outcome
TLR4 is well known for recognizing bacterial lipopolysaccharide. In the study’s multiple-regression analysis, both total bacterial count and endotoxin concentration independently predicted TLR4 activation. That pattern fits the receptor’s expected biology.
TLR2/6 recognizes a broader set of microbial components. Its activation was predicted by total bacterial count but not independently by the measured endotoxin concentration. The same was true for NF-κB and IRF activity, suggesting that the wider mixture of bacterial components mattered more to those readouts than endotoxin alone.
NF-κB and IRFs are transcription factors. They help determine which genes a cell turns up or down after detecting a possible threat. Their activity can influence inflammatory signals, antiviral responses and communication with other immune cells.
Yet these were specialized reporter cells in culture. They were selected precisely because a particular molecular response could be measured cleanly. A human airway contains mucus, resident microbes and many interacting cell types, while a complete immune system includes macrophages, dendritic cells, lymphocytes and organs that no dish can reproduce.
The experiment therefore established that components in sea spray can engage human molecular machinery. It did not establish whether real-world exposure produces a meaningful response in a person, whether that response lasts, or whether its net effect is helpful.
A later study used bronchial cells
A 2025 study moved one step closer to the tissue people actually expose when they breathe. Researchers placed filters within 15 metres of the waterline at Ostend and collected natural sea-spray aerosols monthly for a year. They then exposed human bronchial epithelial cells to extracted material and used RNA sequencing to examine changes across the cells’ gene activity.
According to the study in Environment International, the aerosol samples downregulated activity in the mTOR, PI3K, Akt and NF-κB pathways while upregulating AMPK. These networks help cells coordinate energy use, growth, stress and inflammation.
The direction and number of gene-expression changes varied by sampling month. Those differences correlated with phytoplankton density and the chemical diversity of the aerosol, supporting the idea that marine biology alters what a breaking wave places into the air.
The authors interpreted some of the changes as potentially protective because reduced NF-κB and mTOR-related signalling can be consistent with lower inflammatory and growth-promoting activity, while AMPK helps regulate cellular energy. But pathway names are not diagnoses. The same pathway can have different consequences in different cells, doses and circumstances.
Nor does this later result contradict the 2024 activation experiment. The studies used different samples, cells, doses and endpoints. A receptor can detect a microbial signal while the broader cell later adjusts gene expression in several directions. Biology is a sequence of regulation, not a single on-or-off switch.
Why coastal health is difficult to explain
Studies of blue spaces have often found associations with wellbeing, physical activity or self-reported health. A recent ScienceBlog article on the popular idea of “blue mind” described why that evidence is interesting but heterogeneous. A coast supplies many exposures at once.
People may walk more beside water. They may meet friends, escape traffic noise, receive sunlight or live in neighbourhoods with different income, housing and pollution patterns. The changing sound and view of water may restore attention. Any biological effect of aerosol would be layered on top of these influences.
This makes observational research hard to interpret. If coastal residents report better health, researchers cannot assume spray caused the difference. People choose where to live, access to a clean coast is unequal, and health itself can influence whether someone visits the shore.
The laboratory studies help by demonstrating a possible physical route from ocean biology to human cells. They do not tell researchers how large that route is compared with exercise, stress relief, social contact or lower urban air pollution.
Sea spray is not always benign
Aerosol composition changes with currents, weather, algal blooms, sewage and industrial contamination. A clean stretch of the North Sea in spring is not interchangeable with a polluted estuary, a red-tide beach or wind-blown spray beside a wastewater outfall.
Endotoxin itself can be a potent inflammatory stimulus at sufficient exposure. Marine aerosols can also carry algal toxins and material from contaminated coastal water. Finding a response that might be useful at one concentration does not make all sea spray therapeutic.
Particle size matters as well. Larger droplets tend to deposit in the nose and upper airway. Smaller particles can travel deeper into the respiratory tract, and wind can carry them well beyond the line of breaking waves. The biologically relevant exposure is therefore not captured simply by distance from the water.
These complexities argue against advice to seek sea air as a treatment. The studies did not test patients, compare disease rates or show that more exposure is better. They also do not override local warnings about poor air, harmful algal blooms or contaminated water.
The experiment still missing
Researchers now need measurements that connect the chain. How many particles do coastal residents actually inhale across seasons? Which microbial and organic components reach different parts of the airway? What molecular responses follow at realistic doses, and do those changes correspond to a measurable health outcome?
More sophisticated airway cultures can add mucus, multiple cell types and three-dimensional tissue structure. Controlled exposure studies could monitor short-term biomarkers in volunteers. Long-running population work could combine personal aerosol sensors, time spent near surf, water quality and clinical outcomes rather than relying only on a home address or self-reported health.
Geography will be essential. The Ostend experiments are valuable precisely because the samples were characterized carefully, but one coast in Belgium cannot represent the planet’s shorelines. Warm tropical water, polar seas, enclosed bays and urban beaches each host different chemistry and microbial communities.
For now, the strongest conclusion is modest. Breaking waves place biologically active marine material into the air, and human cells can detect and respond to it. That is a credible mechanism worth pursuing, not confirmation that the ocean breeze is medicine.