Microfoam is a dense, uniform foam made of tiny bubbles, typically smaller than visible to the naked eye. The term shows up in two very different worlds: coffee culture, where it refers to the silky steamed milk in lattes and cappuccinos, and medicine, where it describes a specialized injectable foam used to treat varicose veins. In both cases, the defining feature is the same: bubbles so small and evenly distributed that the foam behaves almost like a liquid, with a smooth, velvety texture rather than a bubbly froth.
Microfoam in Coffee and Milk
When baristas talk about microfoam, they mean steamed milk with bubbles so fine you can barely see them individually. The result is a glossy, paint-like texture that pours smoothly and holds its shape in latte art. This is different from the stiff, dry foam on a traditional cappuccino, which has larger, more visible bubbles and sits on top of the drink in a distinct layer.
The science behind milk microfoam comes down to proteins acting as natural stabilizers. Milk contains two main protein families: caseins (about 80% of total protein) and whey proteins (about 20%). Both are amphiphilic, meaning one end of the molecule attracts water while the other repels it. When steam forces air into milk, these proteins migrate to the surface of each tiny bubble and form a thin film around it, preventing bubbles from merging and popping. This is essentially the same mechanism that makes soap bubbles hold their shape, except the surfactant here is protein instead of detergent.
Temperature matters enormously. Research on steam-frothed milk has found that the optimal finishing temperature for stable microfoam is between 50°C and 60°C (roughly 122°F to 140°F). At 60°C, bubbles in pasteurized whole milk were especially well distributed. Go much hotter, and the whey proteins start to break down in ways that destabilize the foam. Caseins are more heat-resistant than whey proteins, which is partly why overheated milk still foams but produces a coarser, less stable result. Pasteurized whole milk consistently outperforms ultra-high-temperature (UHT) milk for foam stability, producing microfoam that holds up for the 10 to 15 minutes it takes to drink a cappuccino.
Medical Microfoam for Varicose Veins
In medicine, microfoam refers to a foam version of a liquid drug called polidocanol, used to treat varicose veins through a procedure known as sclerotherapy. Polidocanol is an alcohol-based compound that damages the inner lining of veins on contact, causing them to collapse and eventually be reabsorbed by the body. Turning this liquid into a foam dramatically improves how well it works.
The reason is straightforward: when you inject a liquid into a vein full of blood, the blood quickly dilutes the drug and plasma proteins deactivate it before it can do much damage to the vein wall. Foam, by contrast, displaces the blood. It pushes the blood aside and holds the active drug in direct contact with the vein lining long enough to destroy the cells there. This prolonged contact is what makes foam sclerotherapy so much more effective than the liquid version.
The numbers bear this out. In comparative studies, foam sclerotherapy achieved a success rate of about 76% for closing saphenous veins (the large veins in the leg most commonly affected by varicose disease), compared to roughly 40% for liquid sclerotherapy. That’s nearly double the effectiveness from the same drug, just delivered in a different physical form.
How Medical Microfoam Is Made
There are two approaches. The simpler one, sometimes called “physician-compounded foam,” involves mixing polidocanol liquid with room air by rapidly pushing the mixture back and forth between two syringes connected by a stopcock. This produces a usable foam, but the bubble sizes vary widely and the gas-to-liquid ratio (anywhere from 1:1 to 8:1 depending on the doctor’s technique) isn’t standardized. The gas in this foam is essentially room air: 79% nitrogen and 21% oxygen.
The pharmaceutical-grade version, sold under the brand name Varithena, takes a more controlled approach. It uses a pressurized canister that dispenses foam with a consistent bubble size and density. The key difference is the gas composition: instead of nitrogen-heavy room air, it uses a mixture of oxygen and carbon dioxide with only trace amounts of nitrogen (0.01% to 0.08%). This matters because oxygen and carbon dioxide are rapidly absorbed by the bloodstream, while nitrogen lingers. A foam that dissolves quickly after doing its job reduces the risk of gas-related complications.
What the Procedure Feels Like
Microfoam sclerotherapy is an outpatient procedure, meaning you go home the same day. The foam is injected through a needle directly into the problem vein, typically guided by ultrasound so the doctor can watch the foam travel through the vessel. After the injection, you lie down for about 15 minutes so your provider can monitor for any immediate reactions.
You can drive yourself home afterward and return to normal activities right away. Walking is actually encouraged during recovery because it promotes blood flow through the healthy veins. You’ll wear compression stockings or wraps for three to seven days to keep pressure on the treated veins. Anti-inflammatory medications like aspirin and ibuprofen should be avoided for 48 hours after treatment.
Results aren’t instant. The treated veins take weeks or sometimes months to fully fade as your body gradually breaks them down and reabsorbs the tissue.
Risks and Side Effects
The most common side effects are mild and localized: bruising, swelling, warmth, and discomfort around the injection site. Some people develop temporary skin darkening or small sores where the needle entered.
Less common but worth knowing about are visual disturbances. Tiny gas bubbles can briefly enter the bloodstream and cause flashes in the eyes, headaches, nausea, or lightheadedness. These symptoms typically resolve on their own without treatment.
Blood clots in the treated vein occasionally need to be drained. Rarely, a clot can migrate to a deeper vein in the leg, a condition called deep vein thrombosis. Even more rarely, that clot can travel to the lungs, causing a pulmonary embolism. This is a serious but very uncommon complication. Allergic reactions to polidocanol are possible but also rare.
Why Foam Outperforms Liquid
The physical properties that make microfoam effective in both coffee and medicine share a common principle: surfactants lowering surface tension to create and stabilize tiny bubbles. In milk, the surfactants are proteins. In medical foam, the surfactant is polidocanol itself, which has a molecular structure with both water-attracting and water-repelling ends. This dual nature lets it sit at the boundary between gas and liquid, stabilizing each bubble while simultaneously being the active drug.
An ideal medical microfoam needs to be cohesive enough to push blood aside rather than mixing with it, stable enough to maintain contact with the vein wall until the cells are destroyed, and transient enough to break down quickly afterward to minimize complications. Pharmaceutical-grade microfoam achieves this balance more reliably than hand-mixed versions, producing significantly greater damage to the vein lining in laboratory studies using human vein tissue.