Gold interacts with the human body in strikingly different ways depending on its form. A chunk of pure metallic gold swallowed whole passes through the digestive tract with little absorption, while gold ions dissolved in pharmaceutical salts can suppress immune activity, accumulate in organs, and permanently discolor skin. Engineered gold nanoparticles, meanwhile, can slip past biological barriers that block most substances, including the blood-brain barrier. The story of gold in the body is really a story about size, charge, and chemical state, and those variables determine whether gold is inert, therapeutic, or harmful.
Swallowing Gold
Edible gold leaf on desserts and cocktails is one of the most common ways people encounter gold today. In the European Union, food-grade gold is approved as additive E175, and it has been used decoratively on food for centuries. The reassuring conventional wisdom is that metallic gold is biologically inert and simply exits the body. That is mostly true, but a 90-day mouse study complicates the picture slightly. Mice fed E175 at doses relevant to human consumption showed no organ damage, no detectable harm to the liver, spleen, or intestine, and no genotoxic effects in the colon or liver. However, the food additive did shift the gut microbiota composition in females, increasing certain bacterial ratios and raising levels of several inflammatory signaling molecules in the colon. Males showed decreased production of short-chain fatty acids, which are important for gut health. A reference-grade gold particle used in the same study did not trigger those microbiota changes, suggesting the differences may relate to the specific characteristics of the commercial food additive rather than to gold itself.1BioMed Central. A 90-day oral exposure to food-grade gold at relevant human doses impacts the gut microbiota and the local immune system in a sex-dependent manner in mice – Section: Results
For the occasional gold-flecked pastry or champagne, the practical risk is negligible. The particles are too large to be absorbed in meaningful quantities, and whatever trace amounts do cross the gut lining are far below any threshold associated with toxicity. The mouse study is worth noting mainly because it challenges the blanket claim that edible gold does “absolutely nothing” in the gut. It probably does very little, but the immune and microbiome effects observed in a controlled animal model remind us that “food-grade” does not automatically mean “biologically invisible.”
Gold as Medicine for Arthritis
Long before gold nanoparticles became a research darling, doctors were injecting gold salts into patients. This practice, called chrysotherapy, dates back roughly a century and was once a standard treatment for rheumatoid arthritis. Injectable compounds like sodium aurothiomalate and an oral formulation called auranofin delivered ionic gold into the bloodstream, where it suppressed the overactive immune responses driving joint inflammation. These drugs benefited from decades of clinical use, giving physicians an unusually long track record of observed effects.2PubMed Central. Gold-based therapy: From past to present
Gold salts worked, but they came with a price. Side effects ranged from skin rashes and mouth sores to kidney damage and blood disorders. By the 1990s and 2000s, newer biologic drugs began replacing gold therapy for most rheumatoid arthritis patients. Still, the gold salt era left behind invaluable data about how gold ions behave inside the human body, and those lessons now inform newer research into gold-based compounds for cancer treatment and other inflammatory diseases.
How Gold Interacts with Cells
The biological potency of gold compounds traces largely to a single molecular target: an enzyme called thioredoxin reductase. This enzyme helps cells manage oxidative stress by recycling a key antioxidant protein. Gold compounds are extraordinarily efficient at shutting it down. Both gold(I) and gold(III) compounds inhibit thioredoxin reductase at concentrations far lower than other metal compounds achieve.3Journal of Inorganic Biochemistry. Gold complexes inhibit mitochondrial thioredoxin reductase: consequences on mitochondrial functions Gold achieves this by forming a strong bond with a selenium-containing amino acid in the enzyme’s active site, essentially locking it in the “off” position.4PubMed. Insights on the mechanism of thioredoxin reductase inhibition by gold N-heterocyclic carbene compounds using the synthetic linear selenocysteine containing C-terminal peptide hTrxR(488-499): an ESI-MS investigation
When thioredoxin reductase is blocked, cells lose a critical line of defense against oxidative damage. In mitochondria, this triggers a cascade: the membrane becomes leaky, and a protein called cytochrome c spills out, which is a well-known signal for the cell to self-destruct.5PubMed. Mitochondrial thioredoxin reductase inhibition by gold(I) compounds and concurrent stimulation of permeability transition and release of cytochrome c This mechanism explains both the therapeutic and toxic potential of gold. In an overactive immune cell, pushing toward self-destruction can be helpful; it quiets inflammation. In a cancer cell, the same push can kill the tumor. But in a healthy cell, the same mechanism means damage.
Gold compounds also tamp down inflammation through other routes, including blocking a major inflammatory signaling pathway and scavenging the reactive oxygen molecules that drive tissue damage.6Coordination Chemistry Reviews. Golden keys to inflammation: decoding the anti-inflammatory mechanisms of gold(I) and gold(III) complexes (2010–present)
Where Gold Nanoparticles End Up in the Body
Gold nanoparticles are not just miniature lumps of metal. Their behavior in the body depends dramatically on how small they are and what coats their surface. When injected intravenously, the liver captures the majority of gold nanoparticles, but the degree varies enormously with size. Particles around 200 nanometers are almost entirely trapped in the liver, while particles smaller than about 5 nanometers spread much more widely, reaching the blood, heart, lungs, kidneys, brain, thymus, and even reproductive organs.7Biomaterials. Particle size-dependent organ distribution of gold nanoparticles after intravenous administration The smallest particles essentially have an all-access pass to the body.
Surface charge adds another layer of complexity. Positively charged, negatively charged, and neutrally coated nanoparticles of the same size accumulate in different organs at significantly different levels.8PubMed Central. Particle size-dependent and surface charge-dependent biodistribution of gold nanoparticles after intravenous administration This is actually one of the things that makes gold nanoparticles so interesting for medicine: by tweaking size and surface chemistry, researchers can steer particles toward specific tissues.
Crossing the Blood-Brain Barrier
The blood-brain barrier is one of the most selective gates in the body, blocking nearly all drugs and foreign particles from reaching brain tissue. Ultrasmall gold nanoparticles, around 2 nanometers in diameter, can cross it. This was demonstrated in a laboratory model using human brain cell spheroids composed of six different cell types, where the tiny gold particles successfully penetrated the barrier.9Scientific Reports. Transport of ultrasmall gold nanoparticles (2 nm) across the blood–brain barrier in a six-cell brain spheroid model In animal studies, gold nanoparticles coated with specific targeting molecules penetrated even further into the brain tissue surrounding blood vessels.10PubMed Central. Blood-Brain Barrier Permeable Gold Nanoparticles: An Efficient Delivery Platform for Enhanced Malignant Glioma Therapy and Imaging
This ability opens the door to treating diseases that are notoriously hard to reach, from brain tumors to neurodegenerative conditions. Early-stage research has explored functionalized gold nanoparticles that cross the barrier and reduce the toxicity of amyloid-beta peptides, the protein clumps implicated in Alzheimer’s disease, while actually helping preserve barrier integrity.11Materials Today Bio. Attenuation of blood-brain barrier dysfunction by functionalized gold nanoparticles against amyloid-β peptide in an Alzheimer’s disease-on-a-chip model But the same property that makes barrier crossing exciting for therapy also raises safety questions, because any particle that reaches the brain has the potential to alter neuronal function.
That concern is not purely theoretical. When gold nanoparticles were placed inside mouse neurons, they increased neuronal excitability, lowered the threshold for firing, and aggravated seizure-like electrical activity.12PLoS ONE. Intracellular Gold Nanoparticles Increase Neuronal Excitability and Aggravate Seizure Activity in the Mouse Brain Meanwhile, earlier work found that gold ions released from metallic gold particles placed in brain lesions reduced inflammation, decreased neuron death, and stimulated neural stem cell responses, suggesting a neuroprotective effect.13PubMed. Gold ions bio-released from metallic gold particles reduce inflammation and apoptosis and increase the regenerative responses in focal brain injury The takeaway is that gold’s effect on the brain appears to depend heavily on the form, dose, and context. Gold ions released slowly from a metallic implant may calm inflammation, while nanoparticles internalized by neurons may overstimulate them.
Cancer Treatment with Gold Nanoparticles
One of the most developed medical applications of gold nanoparticles is photothermal therapy for tumors. The concept is straightforward: gold nanorods injected into or near a tumor absorb near-infrared laser light and convert it into intense, localized heat, cooking the cancer cells while leaving surrounding tissue relatively unharmed. In mice with squamous cell carcinoma, this approach produced dramatic tumor shrinkage, with over half of directly injected tumors resorbing entirely and a quarter of those treated by intravenous delivery also disappearing.14Cancer Letters. Gold nanorod assisted near-infrared plasmonic photothermal therapy (PPTT) of squamous cell carcinoma in mice
The shape and size of the gold particle matter. Research comparing different nanorod dimensions found that a roughly 28-by-8 nanometer rod offered the best balance between light absorption and heat conversion for killing oral cancer cells in laboratory experiments.15PubMed Central. The Most Effective Gold Nanorod Size for Plasmonic Photothermal Therapy: Theory and In Vitro Experiments More sophisticated versions of these systems coat the gold rod with a porous silica shell that can carry chemotherapy drugs and targeting molecules, creating a single particle that finds the tumor, heats it, and delivers medication simultaneously.16PubMed. Combined Photothermal Therapy and Cancer Immunotherapy by Immunogenic Hollow Mesoporous Silicon-Shelled Gold Nanorods
When gold nanoparticles are specifically targeted to reach the nucleus of cancer cells rather than just the cytoplasm, they can directly damage DNA, triggering the cell to halt division and die.17PubMed. Nuclear targeting of gold nanoparticles in cancer cells induces DNA damage, causing cytokinesis arrest and apoptosis These approaches remain in preclinical and early clinical stages, but the combination of tumor-targeting precision, heat generation, drug delivery, and immune stimulation makes gold nanoparticles one of the more versatile platforms in experimental oncology.
Gold as a Drug Delivery Vehicle
Beyond their direct tumor-killing properties, gold nanoparticles serve as carriers that ferry drugs to specific locations in the body. Their surfaces are easy to coat with different molecules, allowing researchers to attach targeting agents, drug payloads, and protective coatings all at once.18Advanced Drug Delivery Reviews. Drug delivery using gold nanoparticles A recurring challenge in cancer chemotherapy is drug resistance: some tumor cells learn to pump drugs back out before they can do their work. Gold nanoparticles conjugated with the chemotherapy drug doxorubicin have shown the ability to overcome this resistance in drug-resistant liver cancer cells, achieving higher drug accumulation inside the cells than the free drug alone.19Journal of Biomedical Nanotechnology. Surface Functionalized Gold Nanoparticles for Drug Delivery
Gold nanoparticles have also been explored as carriers for immune-boosting agents used in cancer immunotherapy, taking advantage of their stability and the ease with which their surfaces can be tailored.20PubMed Central. Gold Nanoparticles: Construction for Drug Delivery and Application in Cancer Immunotherapy The particles themselves contribute little toxicity at the doses used for delivery, making them appealing scaffolds compared to some synthetic polymer carriers that can cause their own inflammatory responses.
Allergies and Skin Reactions
Despite gold’s reputation as a hypoallergenic metal, it is actually a relatively common contact allergen. In one study of 355 patients with suspected contact dermatitis, about 5% tested positive for gold allergy, with reactions appearing on the face, eyelids, and sites of direct skin contact.21PubMed. Allergic contact dermatitis to gold A Swedish study that added gold sodium thiosulfate to the standard patch test panel found positive reactions in nearly 9% of over 800 consecutive patients, making gold the second most common contact allergen after nickel.22PubMed. High frequency of contact allergy to gold sodium thiosulfate. An indication of gold allergy?
Gold was named “Contact Allergen of the Year” in 2001, yet the clinical picture remains murky. Patch test reactions to gold can be unusually delayed and long-lasting, and gold can also act as an irritant, making it tricky to distinguish true allergy from irritation. Even when a patient tests positive, the clinical relevance is often unclear; many people with positive patch tests to gold wear gold jewelry without obvious problems.23PubMed. Gold contact allergy: clues and controversies The practical implication is that if you develop unexplained facial dermatitis and you wear gold earrings, gold allergy is worth investigating. But a positive patch test alone does not always mean your jewelry is the culprit.
Chrysiasis, or Turning Blue-Gray
Perhaps the most visually striking effect gold can have on the body is chrysiasis: a permanent blue-gray or mauve discoloration of sun-exposed skin. It occurs in people who have received large cumulative doses of injectable gold salts, typically during chrysotherapy for rheumatoid arthritis. A study of 40 patients treated with intramuscular gold found that 31 developed chrysiasis. Visible skin changes appeared above a threshold equivalent to about 20 milligrams of gold per kilogram of body weight, and the severity increased with cumulative dose.24British Journal of Dermatology. Chrysiasis revisited: a clinical and pathological study
The discoloration begins around the eyes as a mauve tinge and can deepen to slate-gray, spreading to the face, neck, and upper arms. Under a microscope, tiny particles of gold are visible in the skin’s dermis. Ultraviolet light plays a role; the pigmentation is concentrated on sun-exposed areas, and case reports describe chrysiasis being triggered by laser treatments in patients with accumulated gold from prior therapy.25PubMed Central. Q-Switched Alexandrite Laser-induced Chrysiasis Chrysiasis is permanent because the gold deposits are physically lodged in the tissue and the body cannot clear them. Specialized imaging techniques can detect gold deposits even at the level of a few atoms in tissue sections, including in the nervous system of patients who received gold injections.26PubMed. Chrysiasis following gold therapy for rheumatoid arthritis: ultrastructural analysis with x-ray energy spectroscopy This condition is now rare simply because injectable gold therapy has fallen out of favor, but it serves as a vivid reminder that gold, once deposited in tissue, tends to stay put.
How the Body Clears Gold
The body’s ability to eliminate gold depends heavily on the particle’s surface chemistry. Gold nanoparticles coated with polyethylene glycol (a common biocompatible polymer) maintain their dispersed state in the body, allowing them to pass through the liver’s filtration architecture and be captured by hepatocytes, which then eliminate them through the bile duct system into the intestines.27PubMed Central. Surface chemistry governs the sub-organ transfer, clearance and toxicity of functional gold nanoparticles in the liver and kidney Particles with other surface coatings tend to clump together inside immune cells in the liver, trapping them for long periods.
The kidneys provide a second excretion route, but only for particles small enough to pass through the kidney’s filtration units. Positively charged gold nanoparticles are excreted more effectively through both the liver and kidney pathways compared to particles with neutral or negative surface charges.28Chemical & Biomedical Imaging. Mass Spectrometry Imaging Reveals That Gold Nanomaterial Surface Chemistry Affects Transport and Excretion in Mice over Time For larger particles or those with problematic coatings, clearance can take weeks or months, and some fraction may never fully leave the body. This persistence is one of the key hurdles for translating gold nanoparticle therapies from the lab to the clinic.
Breathing In Gold
Most people will never inhale gold particles, but workers in certain manufacturing environments or research labs can be exposed to airborne gold nanoparticles. A 90-day inhalation study in rats found that gold nanoparticles accumulated in the lungs and kidneys in a dose-dependent manner, with a gender-related difference in kidney accumulation. At the highest dose, the lungs showed mild inflammatory changes including increased immune cells in the air sacs.29PubMed Central. Subchronic inhalation toxicity of gold nanoparticles The effects were mild, and lower doses showed no significant pathology, but the study established that inhaled gold does not simply bounce off the lungs; it accumulates there and can provoke a low-grade immune response.
Cell culture experiments add another dimension. Human lung fibroblasts exposed to gold nanoparticles in the lab showed signs of oxidative stress, including increased lipid damage and activation of cellular stress responses. The cells activated autophagy, essentially digesting their own damaged components as a protective measure.30PubMed. Autophagy and oxidative stress associated with gold nanoparticles These findings do not mean gold nanoparticles are acutely toxic to the lungs at everyday exposure levels, but they do flag inhalation as the exposure route with the clearest evidence of potential harm.
Gold in Dentistry
Gold alloy crowns and inlays have been used in dentistry for well over a century, and they remain one of the most durable restorative materials available. Unlike some dental alloys, gold crowns release only trace quantities of metal ions into saliva. A clinical study measuring elemental release from gold crowns found that zinc, copper, palladium, gold, and silver were detectable in patient saliva, with a small increase in zinc release after three months of wear. No adverse effects on the gum tissue or the seal at the crown margin were observed.31PubMed. Elemental ion release from fixed restorative materials into patient saliva The amounts involved are extremely small, and decades of widespread use have not linked dental gold to systemic health effects. The main concern, as with gold jewelry, is the occasional allergic reaction in sensitized individuals, though this is less common from oral exposure than from skin contact.
Gold Nanoparticles You Already Use
If you have ever used a home pregnancy test or a rapid COVID-19 test, you have held gold nanoparticles in your hand. The colored line that appears on lateral flow test strips is produced by gold nanoparticles aggregating on a membrane. When antibodies on the gold particles bind their target, the particles concentrate in a visible band, producing the familiar pink or red line. These assays rely on the fact that colloidal gold is stable, biocompatible, and produces an obvious color change visible to the naked eye without any electronic equipment.32PubMed Central. Gold Nanoparticle-Mediated Lateral Flow Assays for Detection of Host Antibodies and COVID-19 Proteins The technology delivers results within minutes and has been adapted for detecting everything from infectious diseases to food contaminants to veterinary pathogens.33PubMed. Development of a colloidal gold nanoparticle-based lateral flow immunochromatographic (LFI) strip test for detecting Senecavirus A (SVA) antibodies in pigs using non-structural protein In this diagnostic context, the gold particles never enter your body. They sit on a paper strip, doing chemistry at room temperature, which is arguably gold’s most widespread medical role today and the one with the most zero-risk profile for the person using it.