Bubbles form in water whenever gas molecules gather into a pocket large enough to resist the surrounding liquid’s pressure. This can happen because dissolved gas comes out of solution as temperature rises or pressure drops, because a chemical or biological reaction generates new gas, or because water itself turns to vapor during boiling. The specific trigger varies widely, from the gentle stream of bubbles climbing the side of a glass of tap water to the violent vapor pockets created by a boat propeller. What ties every case together is a single physical requirement: something has to give gas molecules a place to congregate and grow.
How a Bubble Gets Started
Water can hold dissolved gases the way a sponge holds water. Oxygen, nitrogen, and carbon dioxide all dissolve into water from the surrounding air, and the amount that stays dissolved depends on temperature and pressure. Warm water holds less gas than cold water, so when you heat a pot on the stove you’ll often see tiny bubbles clinging to the sides well before the water boils. Those bubbles are dissolved air escaping as the water’s capacity for gas shrinks. Similarly, when you open a sealed bottle of sparkling water, the sudden drop in pressure means the liquid can no longer hold all the carbon dioxide that was forced into it at the bottling plant, and bubbles rush out.
But dissolved gas alone isn’t enough to explain where and when bubbles appear. In perfectly smooth, pure water, gas molecules would struggle to assemble into a bubble because the surface tension of the surrounding liquid squeezes tiny gas pockets so hard that they tend to collapse before they can grow. For a bubble to survive its earliest moments, it usually needs a head start.
Why Bubbles Always Seem to Start in the Same Spot
If you watch a glass of soda sitting on a counter, you’ll notice streams of bubbles rising from the same few points on the glass wall, often in neat single-file lines. Those points are nucleation sites, tiny imperfections or particles where gas can accumulate without being crushed by surface tension. Scratches in glass, specks of dust, and microscopic fibers all work. Research on superhydrophilic surfaces has shown that trapped gas cavities confined within rough surface textures act as the dominant preferential sites where new bubbles form.1ACS Nano. Regulating Bubble Nucleation via Gas Cavities on Superhydrophilic Surfaces The rougher or dirtier a surface, the more nucleation sites it offers, and the more bubbles you see.
This is why a brand-new, squeaky-clean glass produces fewer bubbles in your soda than an older glass with fine scratches. Some beer glasses are even laser-etched on the bottom to create a deliberate cluster of nucleation sites, giving the drink a steady column of rising bubbles for visual appeal. The physics is the same whether the surface is engineered or accidental: a tiny gas pocket survives inside a crevice, dissolved gas molecules from the liquid diffuse into it, and once the pocket grows large enough, buoyancy pulls it free as a visible bubble.
The Champagne Case
Champagne and other carbonated drinks offer a particularly well-studied example. Researchers examining bubble formation in champagne glasses found that most bubbles originate not from scratches in the glass itself but from tiny hollow cellulose fibers, bits of lint or cloth fiber stuck to the glass wall.2PubMed. Modeling the kinetics of bubble nucleation in champagne and carbonated beverages When champagne is poured, a small air pocket gets trapped inside each hollow fiber. Carbon dioxide dissolved in the wine then diffuses into that pocket, inflating it until a bubble pinches off from the fiber’s tip and rises. The cycle repeats, sometimes producing a new bubble every second or so from the same fiber.
High-speed video recordings have confirmed this process in detail. The gas pockets trapped in these fibers look like miniature versions of the elongated bubbles that form when gas rises through narrow tubes. The rate at which new bubbles pinch off depends on both the fiber’s geometry and the concentration of dissolved CO₂ in the surrounding liquid, with convection currents around the fiber playing a major role in how fast fresh CO₂ reaches the growing pocket.3Colloids and Surfaces A: Physicochemical and Engineering Aspects. On the 3D-reconstruction of Taylor-like bubbles trapped inside hollow cellulose fibers acting as bubble nucleation sites in supersaturated liquids This is why a freshly poured glass of champagne fizzes vigorously at first but calms down after a few minutes: the CO₂ concentration in the liquid is highest right after pouring and drops as gas escapes into the bubbles and then into the air above.
Boiling and the Role of Heat
When you bring a pot of water to a full boil, the bubbles you see are fundamentally different from those in a glass of soda. Soda bubbles are pockets of dissolved carbon dioxide. Boiling bubbles are pockets of water vapor, formed when the liquid’s temperature reaches the point where water molecules have enough energy to transition into gas throughout the bulk of the liquid, not just at the surface.
As the temperature climbs, the process passes through distinct stages. First, dissolved air escapes (those early small bubbles on the pot wall). Then, at temperatures approaching the boiling point, vapor bubbles begin forming at nucleation sites on the heated surface. As the surface gets hotter, boiling intensifies through recognizable regimes: contact boiling, transition boiling, and eventually film boiling, in which a continuous layer of vapor separates the liquid from the hot surface entirely.4PubMed. Droplet Interactions with Hot Surfaces: Boiling Modes, Leidenfrost Temperature, Dynamics, and Applications That last regime is what produces the Leidenfrost effect, the phenomenon where a water droplet skitters across a very hot pan instead of evaporating instantly. The vapor layer acts as an insulating cushion, and the droplet dances on top of its own steam.
The takeaway for everyday cooking: the rolling bubbles of a boil and the quiet pre-boil bubbles clinging to the pot are two different phenomena. The early ones are gas leaving solution. The later ones are liquid becoming gas. Both need nucleation sites to get going, which is why a scratched, well-used pot often produces a more vigorous boil than a perfectly smooth new one.
Cavitation and Pressure-Driven Bubbles
Not all bubbles form because something gets warmer. Some form because the local pressure drops so fast that the liquid essentially tears apart. This process, called cavitation, creates vapor-filled bubbles in regions where pressure falls to or below the liquid’s vapor pressure.5PubMed Central. Fluid dynamics of acoustic and hydrodynamic cavitation in hydraulic power systems It happens behind fast-spinning boat propellers, inside pumps, and anywhere water is forced through a constriction at high speed.
Cavitation bubbles are short-lived and violent. They collapse almost as quickly as they form, and when they do, they can generate shock waves, intense local heating, and tiny jets of water moving fast enough to pit and erode metal surfaces over time. This is a major engineering headache for turbines, ship propellers, and hydraulic systems, where cavitation damage can shorten equipment life dramatically. On the other hand, the same destructive energy has been harnessed for useful purposes: ultrasonic cleaning baths use cavitation bubbles to blast grime off surfaces, and some water-treatment systems use cavitation to break down contaminants.
Bubbles Inside Your Body
Scuba divers know about bubbles in a very personal way. When you breathe compressed air at depth, the elevated pressure forces extra nitrogen into your blood and tissues. During ascent, as the surrounding water pressure drops, that dissolved nitrogen can come out of solution and form bubbles, much the way carbon dioxide escapes from an opened soda bottle. If the ascent is too fast, those bubbles can grow large enough to block small blood vessels or irritate tissues, producing decompression sickness, commonly known as “the bends.”6PubMed Central. Decompression illness: a comprehensive overview
The question of exactly how and where those first tiny bubbles originate inside the body remains a subject of active research. Homogeneous nucleation, where bubbles form spontaneously in the middle of a fluid without any surface or particle to help, requires far greater pressure differences than divers typically experience. Instead, the leading candidates are heterogeneous nucleation on tissue surfaces and a process called tribonucleation, where gas pockets form when tissues slide against each other (as joints move, for instance). Some researchers have also investigated whether nanobubbles that spontaneously form on hydrophobic surfaces in the body could serve as seeds for larger bubble growth, though whether those nanobubbles can actually expand under decompression conditions is still debated.7Advances in Colloid and Interface Science. A critical review of physiological bubble formation in hyperbaric decompression
Bubbles in Trees
Plants face their own bubble problem. Trees pull water from the soil up through narrow vessels in their wood, called xylem, using a tension-driven system that relies on unbroken columns of water stretching from roots to leaves. When drought conditions intensify, the tension on those water columns increases, and at some point the column can snap, forming a vapor bubble inside the vessel. This is called xylem embolism, and it blocks water transport the way an air bubble in a straw stops you from sipping.
Studies tracking embolism events in real time have found that more than 80% of individual cavitation events in drought-stressed angiosperm trees are discrete, single-vessel failures, temporally isolated from one another rather than cascading all at once.8PubMed Central. Xylem Embolism Spreads by Single-Conduit Events in Three Dry Forest Angiosperm Stems Trees can tolerate a fair amount of this: research on several angiosperm species suggests that the threshold for irreversible hydraulic failure is close to 88% loss of water-transport capacity, far higher than the roughly 50% threshold seen in conifers.9Tree Physiology. Xylem embolism threshold for catastrophic hydraulic failure in angiosperm trees In other words, a broadleaf tree can lose the function of most of its water-conducting vessels before reaching the point of no return. This resilience likely reflects the structural properties of angiosperm wood, though the exact anatomical and physicochemical drivers behind embolism vulnerability are still being worked out.10PubMed. Functional xylem characteristics associated with drought-induced embolism in angiosperms
Electrolysis and Chemically Generated Bubbles
You can also force bubbles into existence by splitting water molecules apart. Pass an electric current through water containing an electrolyte, and hydrogen gas forms at one electrode while oxygen gas forms at the other. These gas molecules nucleate as tiny bubbles on the electrode surfaces, grow, and eventually detach and rise. This process, water electrolysis, is one of the main methods being developed for producing hydrogen fuel.
Bubble behavior on electrodes matters a great deal for efficiency. Bubbles clinging to an electrode’s surface block the liquid from reaching the metal, reducing the active area available for the reaction. Research comparing hydrogen and oxygen bubbles during electrolysis in acidic solutions has found distinct differences in how the two gases nucleate, grow, and detach.11PRX Energy. Oxygen versus Hydrogen Bubble Dynamics during Water Electrolysis at Microelectrodes One strategy for managing this problem is applying ultrasound during electrolysis. Experiments have shown that ultrasonic vibrations can shrink the average bubble diameter from about 72 micrometers down to 17 micrometers and cut the time each bubble sits on the electrode by more than three-quarters, reducing surface coverage from roughly 8% to just 1%.12PubMed Central. Hydrodynamic behavior of bubbles at gas-evolving electrode in ultrasonic field during water electrolysis Smaller bubbles that leave faster mean more electrode stays exposed, which means more efficient gas production.
Bubbles in the Ocean and Climate
Breaking ocean waves are among the most prolific bubble generators on Earth. When a wave crest topples over and crashes into the water below, it drives air beneath the surface in turbulent plumes containing millions of bubbles of all sizes. These bubble plumes do more than create the white froth you see on a stormy sea. They form an additional pathway for gas exchange between the ocean and the atmosphere, operating in parallel to the slower process of gas dissolving directly through the flat sea surface.13Reviews of Geophysics. The Role of Bubbles in Air‐Sea Gas Exchange: A Critical Review
This bubble-mediated gas transfer behaves differently from calm-surface exchange in several ways. It increases sharply and nonlinearly with wind speed because higher winds produce more wave breaking. It also depends on how soluble a gas is, because a bubble has a finite volume and a short lifetime, so less soluble gases like oxygen get a proportionally bigger boost. And because submerged bubbles are squeezed by the surrounding water pressure, they tend to push a little extra gas into solution, nudging dissolved gas concentrations slightly above what you’d expect from surface exchange alone.14PubMed Central. A universal wind-wave-bubble formulation for air-sea gas exchange and its impact on oxygen fluxes For global climate models, getting this bubble contribution right matters because it affects estimates of how much oxygen and carbon dioxide the ocean absorbs from or releases to the atmosphere.
Methane Bubbles From Lake and Ocean Floors
Beneath the muddy bottoms of lakes and coastal seas, microorganisms break down organic matter and produce methane and carbon dioxide. When enough gas builds up in the sediment’s pore spaces, it can coalesce into bubbles and eventually escape upward into the water column, a process called ebullition. This is a major route for greenhouse gases to leave sediments and potentially reach the atmosphere.15Earth and Planetary Science Letters. Release of gas bubbles from lake sediment traced by noble gas isotopes in the sediment pore water
The type of sediment strongly influences how gas accumulates and escapes. Laboratory experiments tracking methane bubble formation in different sediment types identified three stages: first, microbubbles displace mobile water from pores without much gas escaping to the surface; second, larger bubbles form that physically push the surrounding sediment aside, and ebullition picks up; and third, persistent gas conduits develop through the sediment, producing a relatively steady release.16Journal of Geophysical Research: Biogeosciences. The role of sediment structure in gas bubble storage and release Clayey sediments stored the most gas before releasing it in large, episodic bursts, while sandier sediments allowed gas to escape more continuously. External forces matter too: periodic pressure changes from passing waves can trigger bubble escape from shallow gas deposits, with shorter-period, higher-amplitude waves being the most effective at shaking bubbles loose.17Geophysical Research Letters. Methane Bubble Escape From Gas Horizon in Muddy Aquatic Sediment Under Periodic Wave Loading
Nanobubbles That Refuse to Disappear
Classical physics says very small bubbles should not last long. A bubble’s internal pressure rises as its size shrinks, which should drive the gas inside it into the surrounding liquid within milliseconds. Yet experiments over the past two decades have found that nanobubbles, gas pockets only tens to hundreds of nanometers across, can persist in water for remarkably long periods. Bulk nanobubble suspensions have been observed to remain stable for many months with their mean diameter unchanged, showing no signs of the coalescence, breakage, or gradual dissolution that theory predicts.18PubMed. On the Existence and Stability of Bulk Nanobubbles
The leading explanation involves electrical charge. Measurements consistently show that nanobubbles carry a negative surface charge, and this charge appears to remain stable over time. The electrostatic repulsion it creates may prevent neighboring bubbles from merging and may also resist the internal pressure that would otherwise crush the bubble flat. Atomic force microscopy and colloidal force modeling have estimated internal pressures in nanobubbles in the range of 120 to 240 psi, yet the bubbles persist, with bulk suspensions remaining detectable for weeks under sealed storage and gradually declining in concentration over the following month or two.19PubMed. Probing Internal Pressures and Long-Term Stability of Nanobubbles in Water Nanobubbles are now being explored for applications in water treatment, agriculture, and medicine, though the full physics of their stability is still being pinned down.
Medical Microbubbles for Drug Delivery
Engineered bubbles have found a striking medical application. Microbubbles, typically a few micrometers in diameter and stabilized by a thin shell of lipid or protein, are already widely used as contrast agents in ultrasound imaging. But researchers have been developing them as targeted drug-delivery vehicles as well. The idea is to load a drug or gene therapy onto or inside a microbubble, inject it into the bloodstream, and then use a focused ultrasound beam to burst the bubbles precisely at the target tissue.20PubMed Central. The use of microbubbles to target drug delivery
When ultrasound waves hit a microbubble, the bubble oscillates and, at higher intensities, collapses. That collapse can create temporary, reversible openings in cell membranes and the walls of small blood vessels, a process called sonoporation. These openings allow therapeutic agents to cross biological barriers they would normally be blocked by, enabling localized drug delivery without surgery.21PubMed Central. Ultrasound and microbubble guided drug delivery: mechanistic understanding and clinical implications This approach has shown promise for delivering chemotherapy directly to tumors, for pushing gene therapies into heart tissue, and for opening the blood-brain barrier in a controlled way to treat neurological conditions. The bubbles themselves are the delivery mechanism, their formation and destruction carefully choreographed rather than accidental.