Why Do I Smell Like Pennies? The Science Behind the Odor

The penny-like smell on your skin is not actually the scent of metal itself. Metals have no inherent odor that our noses can detect. What you’re smelling are organic compounds, mostly carbon-based molecules called carbonyls, produced when trace amounts of iron or copper react with the oils and fats naturally present on your skin. The chemistry behind this is surprisingly well-studied, and the reasons the smell shows up at certain times in your life range from mundane (you just handled a handful of coins) to medically worth investigating.

Where the “Penny” Smell Actually Comes From

When iron or copper touches your skin, it interacts with lipid peroxides, the breakdown products of oils sitting on your skin’s surface. That reaction rapidly produces volatile carbonyl compounds. Research has identified two of the most important ones: 1-octen-3-one and 1-nonen-3-one. In testing with ferrous sulfate solutions, 1-nonen-3-one turned out to be at least ten times more potent than any other odorant released, making it the primary driver of what we perceive as a metallic smell.¹ The same lipid oxidation process occurs in your mouth when you swallow water with dissolved iron or copper, which is why metallic-tasting tap water and metallic-smelling skin share a common chemical origin.²

Your skin provides the perfect canvas for this reaction. Sebum, the oily substance produced by your sebaceous glands, is rich in lipids that serve as the raw material. Squalene alone makes up roughly 15% of human sebum by weight, and sapienic acid (including its ester forms) accounts for more than 25%.³ These fats are constantly being broken down by bacteria living on your skin and by simple chemical oxidation in air, generating the peroxides that react so readily with metals. Anaerobic bacteria deep in your hair follicles liberate long-chain fatty acids from triglycerides, and aerobic bacteria then metabolize those into smaller volatile acids, aldehydes, and alcohols.⁴ So when you touch a railing, a set of keys, or a pile of coins, you’re supplying the metal catalyst to a skin surface already primed with reactive lipid fragments.

Why the Smell Shows Up After Exercise

A lot of people first notice the metallic smell on their skin after a hard workout. There are a couple of reasons for this. First, your sweat actually contains measurable amounts of iron, copper, and zinc. The concentrations vary depending on where on your body you’re sweating and how hard you’re working. During exercise, estimated whole-body iron losses through sweat roughly doubled compared to rest in one study of athletes, with losses averaging about 0.08 mg per square meter of skin per hour during exercise compared to 0.039 at rest.⁵ Men in that study lost about twice as much iron in sweat as women did.

Those trace metals in sweat then meet the same skin oils described above, and the oxidation reaction kicks off right there on your skin without you having touched any external metal object. The warmer your skin and the more you’re sweating, the more quickly these reactions produce volatile odorants. Second, the increased blood flow to your skin during exercise brings more iron-containing hemoglobin closer to the surface. While hemoglobin stays inside blood vessels under normal conditions, the sheer increase in circulation and minor capillary leaking that happens during intense physical effort can amplify the penny-like smell some people detect. If you notice the scent more on certain body parts, that tracks with research showing that the metal content of sweat varies by body site.⁶

Diet, Ketosis, and Metabolic Shifts

What you eat can change how you smell, and some dietary states produce odors that people describe as metallic. The most well-documented version of this involves ketosis, the metabolic state your body enters when it burns fat instead of carbohydrates for fuel. During ketosis, your liver produces ketone bodies, one of which is acetone. That acetone gets excreted not just through your breath but also through your skin. A controlled crossover study found that skin-emitted acetone was a reliable biomarker of ketosis, accurately distinguishing ketotic from non-ketotic states with an area under the curve of 0.83, performing as well as breath acetone.⁷

Acetone has a sharp, chemical-solvent smell, which some people interpret as metallic. If you’ve recently started a ketogenic or very low-carbohydrate diet, or if you’ve been fasting, skin-emitted acetone is a likely explanation for any new unusual odor. The smell tends to fade as your body becomes more efficient at using ketones for fuel, typically within a few weeks. High-protein diets can also change your body odor through different pathways, as the byproducts of amino acid metabolism alter your sweat composition, though this is less commonly described as specifically “penny-like.”

Medications That Change How You Smell and Taste

Hundreds of medications can induce altered taste and smell, and metallic is one of the most common complaints. Some drugs cause this because of their own chemical properties; others interfere with the way your nervous system processes sensory information. The metallic taste or smell can result directly from a drug’s chemical structure interacting with receptors in your mouth and nose, or indirectly from the drug being excreted in saliva or sweat.⁸

Some of the more commonly reported culprits include:

• Antibiotics: Metronidazole and clarithromycin are particularly well-known for producing a metallic taste that can also alter how your skin smells to you.
• Blood pressure drugs: ACE inhibitors like captopril contain a sulfhydryl group that can produce metallic sensory distortions.
• Chemotherapy agents: Many platinum-based drugs and other chemotherapy medications alter taste and smell through direct nerve effects.
• Lithium: Used for mood disorders, lithium is excreted in sweat and can change body odor.
• Iron supplements: Perhaps the most obvious connection. Oral iron supplements raise iron levels in your saliva and may increase iron in your sweat, directly feeding the skin-lipid oxidation reaction that produces metallic odorants.

If you started a new medication and noticed the smell shortly after, that connection is worth mentioning to your prescribing doctor. The sensory change is rarely dangerous on its own, but it can sometimes be managed with a dose adjustment or a switch to a different formulation.

When a Metallic Smell Could Signal a Health Problem

Most of the time, smelling like pennies is explained by something benign. But persistent metallic body odor that you can’t trace to exercise, diet, or a medication deserves attention, because it can occasionally reflect an underlying condition.

Kidney disease is one of the more serious possibilities. When your kidneys lose their ability to filter waste products efficiently, urea and other nitrogen-containing compounds accumulate in the blood. In severe cases, these waste products get excreted through sweat, and after evaporation, urea can actually crystallize on the skin in a phenomenon called uremic frost.⁹ Even before reaching that extreme stage, the buildup of waste in sweat can produce unusual odors, sometimes described as metallic or ammonia-like. If you also have fatigue, swelling in your legs, or changes in urination, those symptoms together warrant a medical evaluation.

Liver dysfunction can produce a similar effect, since the liver is responsible for processing many of the compounds that influence body odor. Poorly controlled diabetes, beyond the ketosis mechanism discussed earlier, can alter sweat composition in ways that some people perceive as metallic. And while rare, certain metal-storage disorders like hemochromatosis (iron overload) can theoretically contribute, since excess iron in the body has more opportunities to react with skin lipids.

When the Smell Is in Your Nose, Not on Your Skin

Before assuming the smell is coming from your body, it’s worth considering whether you might be perceiving a metallic odor that isn’t physically there. Phantosmia, the experience of smelling something with no external source present, is more common than most people realize. Population-based research has found that phantom smells affect a meaningful share of adults, with metallic and burning odors among the more frequently reported types.¹⁰

One surprisingly common contributor to metallic taste and smell distortions is zinc deficiency. Zinc plays a critical role in how your taste buds and olfactory neurons function. Patients who are deficient in zinc, regardless of what caused the deficiency, frequently experience taste dysfunction, and treatment with zinc typically improves symptoms.¹¹ That taste dysfunction often manifests as a persistent metallic, bitter, or sour sensation.¹² Because taste and smell are so intertwined, a metallic taste in your mouth can easily be misinterpreted as a metallic smell on your skin, especially if you bring your hand to your face frequently.

Other neurological causes of phantom metallic smells include migraines (which can have an aura that includes olfactory distortion), head injuries, sinus infections, and in rare cases, temporal lobe seizures. If the smell comes and goes in episodes, particularly if it precedes a headache or occurs alongside other sensory changes, a neurological explanation is more likely than a dermatological one.

Pregnancy and Heightened Smell Perception

Pregnant women frequently report that their sense of smell changes, sometimes dramatically, and metallic odors are among the common complaints. The popular explanation is that pregnancy hormones sharpen olfactory sensitivity, but the scientific evidence is more complicated. A thorough review of the research found that support for a genuine decrease in olfactory thresholds during pregnancy is “generally lacking.” What does change, according to limited evidence, is how odors are experienced emotionally: pregnant women may rate certain smells as more unpleasant or intense without actually detecting them at lower concentrations.¹³

This means that if you’re pregnant and suddenly aware of a metallic smell on your skin, you may not be producing more metallic odorants than usual. Instead, the same low-level skin chemistry that was always happening may now register as more noticeable or more bothersome because your hedonic response to the odor has shifted. Pregnancy also involves significant increases in blood volume and changes in iron metabolism, which could contribute additional iron to sweat. Combine that with the emotional amplification of smell perception, and it makes sense why so many pregnant women report this particular complaint even when nothing is objectively different about their skin chemistry.

Why Humans Are Remarkably Good at Detecting This Smell

One reason the metallic smell catches your attention so readily is that humans appear to be evolutionarily tuned to detect it. Research comparing olfactory sensitivity across species found that humans are more sensitive to trans-4,5-epoxy-(E)-2-decenal, a key volatile component of the smell of blood, than mice are. That finding surprised researchers, because mice have far more olfactory receptor neurons and a proportionally larger area of olfactory tissue. The study’s authors suggested that behavioral relevance, not neuroanatomical hardware, determines how sensitive a species is to a particular odorant.¹⁴

The implication is that being able to smell blood, and by extension the iron-lipid reaction products that share overlapping chemistry, was important enough to our ancestors that natural selection honed our sensitivity to it. Detecting blood quickly would have been useful for finding injured prey, avoiding predators, recognizing wounds in group members, and identifying contaminated food or water. The metallic “penny” smell you notice on your hands sits on the same chemical continuum as the smell of blood, which is why it registers so strongly even at very low concentrations. You’re not being overly sensitive. Your nose is doing exactly what it evolved to do.

Practical Steps When the Smell Bothers You

If you’ve figured out the trigger and just want to manage the smell, a few things help. After handling coins, keys, weights, or iron cookware, washing your hands with soap and water removes the volatile carbonyls quickly. Stainless steel “soap bars,” those metal-shaped blocks sold for removing garlic odor, work on the same principle: they provide a surface for residual odorants to bind to and wash away. After exercise, showering promptly and using a soap that emulsifies skin oils will remove the lipid peroxides before they can keep reacting with trace metals in your drying sweat.

For diet-related causes, the smell from ketosis usually resolves on its own as your body adapts, but staying well-hydrated can dilute the acetone excretion rate. If a medication is the culprit, switching to a coated or extended-release formulation sometimes reduces the effect, particularly with iron supplements, which are available in several different salt forms that vary in their tendency to cause metallic taste.

If the smell is persistent and you can’t pin it to an obvious external cause, a basic blood panel checking kidney function, liver function, iron levels, and zinc status covers the most likely medical explanations. Mentioning the symptom to your doctor might feel silly, but changes in body odor are legitimate clinical information, and they occasionally lead to catching something early that would otherwise have gone unnoticed.

The Skin Microbiome’s Role in Individual Variation

Even when two people handle the same set of coins, one may notice the metallic smell intensely while the other barely detects it. Part of this comes down to differences in the skin microbiome. The specific bacterial communities living on your skin determine which volatile organic compounds are produced from your sebum. Bacteria that are more active in breaking down triglycerides into short-chain fatty acids and aldehydes will generate more lipid peroxide precursors, giving metals more material to react with.⁴ Meanwhile, some of the most distinctive components of body odor originate from sebum precursors through reactions that don’t involve bacteria at all, through simple auto-oxidation in air.³

Your genetics, your diet, your hygiene products, and even the humidity of the environment you live in all shape which bacteria thrive on your skin and how much sebum you produce. This is why the metallic smell can vary between people, between body sites on the same person, and even from day to day. Someone with oilier skin will generally produce more lipid oxidation products and notice the smell more intensely after touching metal. Someone with drier skin, or who recently exfoliated, may barely notice it at all. The variability isn’t mysterious once you understand that the smell isn’t coming from the metal. It’s coming from you, and no two people’s skin chemistry is identical.