What Are Liposomes and How Do They Work?

Liposomes are tiny hollow spheres made of the same type of fat molecules that form the membranes of your cells. Because of this similarity, they can carry drugs, vitamins, or genetic material through the body and deliver it where it is needed, all while being naturally broken down and recycled by the body’s own processes. First described in the 1960s, liposomes have since become the most widely used nanocarriers in medicine, prized for their compatibility with human tissue, their ability to hold both water-soluble and fat-soluble payloads, and the many ways their surfaces can be customized for specific jobs.

The Basic Structure

A liposome forms when phospholipids, the same molecules that make up cell membranes, are mixed with water. Each phospholipid has a water-loving head and a fat-loving tail. In water, these molecules spontaneously arrange themselves into a double layer (a bilayer) that curves into a closed sphere. The watery interior can hold water-soluble substances, while the oily bilayer itself can hold fat-soluble ones. This dual-compartment design is one reason liposomes are so versatile as carriers.

Liposomes come in several structural varieties. Some have a single bilayer shell and are relatively small, while others have multiple concentric shells, like the layers of an onion. There are also multivesicular types, which contain smaller vesicles nested inside a larger one. These differences in size and layering affect how much cargo a liposome can hold, how quickly it releases that cargo, and how it behaves in the body.¹

A Brief Origin Story

The British blood scientist Alec Bangham stumbled onto liposomes in 1961 while studying phospholipids and blood clotting under an electron microscope at the University of Cambridge. The images he and his colleague R.W. Horne captured were the first visual proof that lipid molecules naturally form bilayer structures, confirming what had been theorized about cell membranes. By the early 1970s, researcher Gregory Gregoriadis proposed that these self-assembling spheres could be loaded with drugs and used as delivery vehicles, kicking off decades of pharmaceutical development.²

How Drugs Get Loaded Inside

Getting a drug into a liposome is not as simple as stirring the two together. There are two broad strategies: passive loading and active (or remote) loading. Passive loading means the drug is present during liposome formation and gets trapped inside as the bilayers assemble. This works reasonably well for some compounds, but often results in low trapping efficiency because much of the drug stays outside.

Active loading is more elegant. A chemical gradient is set up across the liposome membrane, and the drug is drawn inward by that gradient after the liposomes have already formed. One classic technique uses ammonium sulfate gradients. The drug crosses the membrane, encounters the internal environment, and becomes trapped at concentrations far higher than exist outside. For the chemotherapy drug doxorubicin, this method achieves loading efficiencies above 90%, concentrating the drug inside the liposome at levels up to 100-fold higher than the surrounding solution.³

How Liposomes Are Manufactured

The traditional way to make liposomes in a lab is called thin-film hydration. Lipids are dissolved in a solvent, which is then evaporated to leave a thin film on the wall of a flask. Adding water causes the lipid film to peel off and form liposomes. The resulting vesicles are usually uneven in size, so they need additional processing, like being pushed through membranes with tiny pores (extrusion), to make them uniform.

A newer approach uses microfluidic devices, which precisely mix lipid solutions and water in microscopic channels. Compared to the traditional method, microfluidics produces liposomes that are significantly smaller and more uniform, with higher drug-loading efficiency.⁴ One study found that the microfluidic approach produced vesicles about 2.5 times smaller than those made by thin-film hydration, with double the loading capacity for a photosensitizing agent. The ability to control particle size by adjusting flow rates gives manufacturers much tighter quality control, which matters when consistent dosing is the goal.⁵

Getting Inside Cells

Once liposomes reach their target, they still need to deliver their cargo into cells. The dominant route is endocytosis: the cell membrane wraps around the liposome, pulls it inside into a small internal compartment, and eventually breaks it down, releasing the payload. Most liposomes, like most other nanocarriers, end up inside cellular recycling compartments called lysosomes.⁶

Some specially designed liposomes can fuse directly with the cell membrane instead, merging their lipid shell with the cell’s outer membrane and dumping their contents straight into the interior of the cell. Research has shown that these fusogenic liposomes trigger a distinct, strong calcium signal inside the cell at the moment of fusion, while liposomes entering by endocytosis produce weaker, repeated calcium signals.⁷ Direct fusion is attractive because it bypasses the lysosome, where acidic conditions can degrade fragile payloads before they reach their target inside the cell. Even cationic liposomes designed for gene delivery, though they interact strongly with cell membranes, still enter primarily through endocytosis.⁸

Stealth Liposomes and the PEG Shield

Plain liposomes injected into the bloodstream get gobbled up quickly by immune cells, especially in the liver and spleen. This rapid clearance limits how much drug actually reaches the intended site. The breakthrough solution was coating the liposome surface with a polymer called polyethylene glycol, or PEG. The PEG chains create a water-loving “brush” layer that makes the liposome nearly invisible to the immune system’s cleanup crew, earning these particles the nickname “stealth liposomes.”⁹

PEGylation dramatically extends the time a liposome circulates in the blood, from minutes to hours or even days. This longer circulation time gives the liposome more chances to accumulate at sites of disease, particularly in tumors, where leaky blood vessels allow nanoparticles to seep through and become trapped. The PEG shield is now standard in most clinical liposome formulations.¹⁰

Targeted and Trigger-Activated Delivery

Stealth technology keeps liposomes in circulation longer, but it does not guide them to a specific tissue. For that, researchers attach targeting molecules, called ligands, to the liposome surface. These can be antibodies, short protein fragments (peptides), sugar molecules, or aptamers (short strands of nucleic acid that bind specific proteins). Each type of ligand recognizes a particular receptor on the surface of a target cell, so the liposome homes in on, say, a cancer cell that overexpresses a certain receptor while largely ignoring healthy tissue.¹¹ In studies, these targeted liposomes show greater selectivity for cancer cells, deliver more drug to tumors, and cause fewer side effects compared to untargeted versions or free drug.¹²

An additional layer of control comes from stimuli-responsive designs. Temperature-sensitive liposomes, for example, remain stable at normal body temperature but release their contents when heated a few degrees above normal, a condition that can be induced locally at a tumor site using focused ultrasound or other external energy sources.¹³ Other versions respond to the slightly acidic environment found inside many tumors, or combine both pH and temperature sensitivity into a single particle. One such dual-sensitive design showed sustained drug release in acidic, warm conditions while remaining stable under normal physiological conditions.¹⁴

Liposomal Doxorubicin in Cancer Treatment

The most commercially successful liposome drug is pegylated liposomal doxorubicin, sold as Doxil or Caelyx. Doxorubicin is a powerful chemotherapy agent, but in its conventional form it is notoriously toxic to the heart. Wrapping it in PEG-coated liposomes changed the risk profile. A meta-analysis of randomized trials found that liposomal doxorubicin cut the odds of cardiotoxicity roughly in half compared to conventional doxorubicin in advanced breast cancer.¹⁵

A separate large meta-analysis confirmed the heart-protection benefit more broadly: heart failure was about three times less common in patients receiving liposomal doxorubicin, and significant drops in heart pumping function occurred less than half as often, compared to other anthracycline-based therapies. Tumor response and overall survival were equivalent between the two approaches.¹⁶ Patients who had already received anthracycline treatment before were especially vulnerable to cardiac damage from conventional doxorubicin; in that subgroup, the cardiac risk was roughly seven times higher with conventional treatment than with the pegylated liposomal version.¹⁷

Fighting Dangerous Fungal Infections

Cancer treatment is not the only area where liposomes have proven their worth. Amphotericin B, a critical antifungal drug used against life-threatening infections, is infamous for damaging the kidneys. Liposomal amphotericin B (sold as AmBisome) wraps the drug in liposomes, dramatically reducing its kidney toxicity while preserving its antifungal power. Multiple randomized trials have clearly shown that the liposomal version causes significantly less kidney damage than the conventional formulation.¹⁸ Kidney toxicity still occurs at some rate, but it is a fraction of what patients experienced with the older form.¹⁹

From Liposomes to mRNA Vaccines

If you received a COVID-19 mRNA vaccine, you encountered a close relative of the liposome. The lipid nanoparticles (LNPs) used by Pfizer-BioNTech and Moderna evolved directly from liposome technology. While liposomes are the “early version” of lipid-based nanocarriers, LNPs feature more complex internal structures optimized for wrapping and protecting fragile nucleic acids like mRNA.²⁰ The core principle is the same: lipid shells protect their payload from degradation, help it cross cell membranes, and can be engineered for specific delivery profiles. The success of mRNA vaccines brought decades of quiet liposome research into the global spotlight overnight.

Liposomal Supplements

Walk through a health food store and you will find liposomal vitamin C, glutathione, and curcumin on the shelves. The marketing claim is straightforward: wrapping a nutrient in liposomes helps more of it reach your bloodstream. For vitamin C, the evidence is actually reasonably supportive. A scoping review of pharmacokinetic studies found that all but one showed higher blood levels of vitamin C from liposomal formulations, with peak concentrations roughly 1.2 to 5.4 times higher and total absorption 1.3 to 7.2 times higher than non-liposomal vitamin C at similar doses.²¹

A double-blind, placebo-controlled trial confirmed these findings, reporting that a liposomal vitamin C formulation significantly raised both plasma and white blood cell vitamin C levels compared to standard vitamin C and placebo.²² The liposomal shell likely protects vitamin C from degradation in the digestive tract and improves its absorption through the gut lining. That said, whether higher blood levels translate into meaningful health benefits over standard supplementation is a different question, and one that has not been conclusively answered. Higher absorption does not automatically mean better health outcomes.

Immune Complications With PEGylated Liposomes

PEG coatings solve the rapid-clearance problem, but they introduce some problems of their own. The most studied is the accelerated blood clearance (ABC) phenomenon: after a first dose of PEGylated liposomes, the body produces antibodies against PEG. When a second dose is given, those antibodies latch onto the PEG-coated particles and trigger the immune system’s complement cascade, clearing the liposomes from the blood far faster than the first dose. This reduces how much drug reaches its target and raises the risk of side effects.²³

A related issue is a type of infusion reaction called CARPA (complement activation-related pseudoallergy). In animal models, anti-PEG antibodies binding to PEGylated liposomes activate complement proteins through a specific pathway, which can cause symptoms resembling an allergic reaction, including flushing, shortness of breath, and changes in blood pressure.²⁴ Researchers are actively working on alternatives. One promising approach uses branched “Y-type” PEG molecules instead of the standard linear form. In animal studies, liposomes coated with Y-type PEG triggered far lower antibody production and avoided activating the complement system, essentially sidestepping the ABC problem on repeat dosing.²⁵

Biomimetic Liposomes Disguised as Cells

One of the more inventive directions in liposome research is coating them with real cell membranes. The idea is that a liposome dressed in the membrane of a natural killer cell, a macrophage, or even a tumor cell will be treated by the body the way it would treat the original cell. Natural killer cell membrane-coated liposomes, for instance, retain the surface receptors that help NK cells find tumors, giving the liposome an inherent tumor-targeting ability while also appearing non-threatening to the immune system.²⁶

Macrophage membrane-coated liposomes have been developed for brain tumors, taking advantage of the natural ability of macrophages to cross the blood-brain barrier and accumulate at tumor sites. These particles also showed reduced uptake by other macrophages, suggesting effective immune evasion.²⁷ Perhaps the most counterintuitive approach is tumor cell membrane camouflage: wrapping liposomes in the membrane of the very cancer cells they are meant to destroy. Cancer cells of the same type tend to stick together through surface adhesion molecules, so a liposome disguised as a lung cancer cell gets preferentially taken up by other lung cancer cells. The tumor-cell coat also carries CD47, a “don’t eat me” signal that discourages immune cells from clearing the particle prematurely.²⁸

Liposomes in Skincare

Outside of medicine, liposomes have carved out a niche in the cosmetics industry. Skin creams and serums use liposomes to carry active ingredients like vitamins, retinoids, and moisturizing agents past the outer skin barrier and into deeper layers. Because the liposome bilayer closely resembles the lipid structures in skin, these particles can merge with the skin’s natural barrier rather than simply sitting on top of it. This improves the delivery of active ingredients, boosts hydration, and helps stabilize compounds that might otherwise degrade when exposed to air or light.²⁹ The effectiveness varies widely depending on the formulation, though, and “liposomal” on a label is not a guarantee that the product performs meaningfully better than a well-made conventional cream.

Why Manufacturing and Regulation Remain Difficult

For all their promise, liposomes are not simple to make at pharmaceutical scale. Regulatory agencies require a long list of characterization data before a liposomal drug can be approved: particle size, surface properties, how much drug is encapsulated versus free, the drug-to-lipid ratio, membrane transition temperature, drug leakage rates over the product’s shelf life, and how the formulation behaves under varying salt concentrations, pH, and temperatures. Every batch produced at manufacturing scale must be validated for consistency.³⁰

This complexity creates a high barrier to entry. Unlike a conventional pill, where you are mostly measuring how much active ingredient is present, a liposomal drug is a composite system where the carrier itself affects the drug’s behavior. A slight change in lipid composition, preparation method, or storage conditions can alter how quickly the drug leaks out, how the particle interacts with the immune system, and ultimately how the drug performs in a patient. Generic versions of liposomal drugs face the same hurdle: showing that a copy truly behaves like the original is far harder than proving two tablets contain the same amount of the same chemical. This is one reason the field has advanced more slowly than its early promise suggested, and why the products that have reached the market represent only a fraction of what has been explored in the lab.