Buying used shoes is generally safe for most people, provided you inspect them carefully and clean them before wearing. The real risks fall into two categories: microbial contamination (fungi and bacteria left behind by the previous wearer) and altered biomechanics (worn-down cushioning and molded footbeds that match someone else’s gait). Neither risk is extreme for a healthy adult buying a lightly used pair, but both deserve more attention than most secondhand shoppers give them.
The Germ Question
Feet are warm, often damp, and enclosed for hours at a time, which makes shoes a hospitable environment for microorganisms. The inside of a shoe can harbor dermatophytes (the fungi behind athlete’s foot and toenail infections), yeasts, bacteria that produce odor, and occasionally viruses like the human papillomavirus strains responsible for plantar warts. A study of athletes’ footwear found that while bacterial loads could be reduced with sanitizing techniques, yeasts and molds proved stubbornly persistent and showed no statistically significant decrease after treatment.1PubMed Central. Is it possible to sanitize athletes’ shoes? That finding underscores a practical point: the organisms most associated with foot infections are also the hardest to scrub out of shoe materials.
Viruses present a somewhat different picture. Plantar warts are caused by HPV strains that thrive in moist environments. Research on schoolchildren found that sharing shoes was one of several factors significantly associated with higher wart prevalence, alongside walking barefoot and living in crowded households.2PubMed Central. Prevalence and factors associated with warts in primary school children in Tema District, Sohag Governorate, Egypt That study looked at direct sharing rather than secondhand buying, and the viral load in a shoe that has sat idle in a thrift store for weeks is far lower than in one passed back and forth daily. Still, a shoe with a visibly damp or degraded insole warrants more caution than one that is clean and dry.
For a healthy adult with intact skin on the feet, the practical infection risk from a cleaned pair of used shoes is low. The concern escalates for people with open cuts, cracked heels, compromised immune systems, or existing fungal infections, all of which give pathogens an easier point of entry.
What Worn-Down Soles Do to Your Feet
This is the risk that most people overlook entirely. Every shoe gradually molds to the gait pattern of the person wearing it: the midsole compresses unevenly, the outsole wears down more on one side, and the insole develops a footprint shaped by someone else’s arch and body weight. When you slip into a shoe that has already been broken in by another person, you are stepping into their biomechanical signature, not yours.
A finite element analysis of running shoes with simulated external wear found that progressive sole wear shifted heel pressure toward the medial side and expanded the high-pressure area during neutral landings, raising peak pressure by roughly 24% and increasing calcaneus stress by about 23%.3PubMed. The influence of simulated worn shoe and foot inversion on heel internal biomechanics during running impact Those are not trivial numbers if you are running regularly or spending long hours on your feet. Another study found that worn-out shoes increased the energy cost of walking and reduced lower-leg stability, and that after about 30 minutes of walking, the shoes’ ability to absorb impact began to deteriorate further.4Podiatry Arena. Effects of worn out shoes
The takeaway is not that every used shoe will hurt you. A dress shoe worn a handful of times to weddings is barely broken in. A running shoe that has logged hundreds of miles, on the other hand, has already used up the lion’s share of its cushioning life, and buying it used means you are getting the tail end of its useful span.
How Fast Cushioning Actually Degrades
The midsole foam in most athletic shoes is the component that deteriorates fastest and matters most for impact protection. Testing of running shoes found that they retained about 75% of their initial shock absorption after 50 miles, dropped to around 67% after 100 to 150 miles, and fell below 60% somewhere between 250 and 500 miles.5PubMed. Shock absorption characteristics of running shoes A separate study examining EVA foam midsoles found that peak plantar pressure doubled after about 500 kilometers of running, and scanning electron microscopy revealed visible structural damage to the foam, including wrinkling and holes, after 750 kilometers.6PubMed. Heel-shoe interactions and the durability of EVA foam running-shoe midsoles
The challenge for a secondhand buyer is that you cannot see midsole fatigue the way you can see a worn-down outsole. A shoe can look nearly new on the outside while its foam is already compressed past the point of meaningful cushioning. This is why athletic shoes and daily walking shoes are the riskiest categories to buy used, while shoes worn infrequently, like formal footwear or seasonal boots, tend to retain much more of their structural integrity.
Chemical Residues You Might Not Think About
Shoes contain a surprising number of industrial chemicals, and some of them are not benign. An ecotoxicological study of shoe soles found that they contained substances toxic to test organisms, with the toxicity primarily attributable to zinc.7PubMed. Chemical risks and consumer products: the toxicity of shoe soles More recently, a broad investigation of clothing and footwear sold in the EU found that about 19% of tested items could represent a significant source of consumer exposure to phthalates and polycyclic aromatic hydrocarbons due to non-compliance with EU safety regulations.8PubMed. Unveiling the Chemical Safety of Clothing Articles, Textiles and Footwear With Regard to the Presence of Carcinogenic, Mutagenic, or Reprotoxic Substances, Endocrine Disruptors and Skin Sensitizers Under EU Regulatory Restrictions
In practice, this concern applies equally to new and used shoes, sometimes more so to new ones. Chemical off-gassing from adhesives, dyes, and rubber compounds is typically highest when a shoe is brand new, and many of those volatile compounds diminish with time and exposure to air. A used shoe that has been worn and aired out may actually carry a lower chemical load than a fresh one straight from the box. The exception would be shoes that have absorbed external contaminants, like motor oil, pesticides, or industrial chemicals, during their previous life. If a used shoe smells unusual or comes from an unknown industrial setting, skip it.
Children and People with Diabetes
Two groups deserve special mention because the stakes are meaningfully higher for them.
Children’s feet are still developing, and the footwear they wear during growth periods can influence arch formation and overall foot morphology. Research comparing habitually barefoot and habitually shod children found that habitual footwear use had significant effects on foot-related outcomes across all age groups, including changes to arch shape and hallux angle, with potential long-term consequences for motor learning and health.9PubMed Central. Growing-up (habitually) barefoot influences the development of foot and arch morphology in children and adolescents A used shoe that has already been molded to another child’s foot imposes that child’s structural pattern on the new wearer. For a toddler whose arch and gait are still forming, stepping into shoes pre-shaped by someone else’s feet is a worse gamble than it would be for an adult whose foot structure is already set. Children also outgrow shoes quickly, so used kids’ shoes are often barely worn and perfectly fine, but heavily used ones are worth avoiding.
For people with diabetes, footwear fit is a clinical concern, not just a comfort preference. Estimates suggest that somewhere between a third and over 80% of people with diabetes wear improperly fitting shoes, which causes microtraumas that lead to excessive pressure and friction on the foot and can trigger skin ulcers.10PubMed Central. What Footwear Do People with Diabetes Mellitus Use? A Narrative Review When peripheral neuropathy reduces sensation in the feet, a person may not feel the irritation from a shoe that doesn’t fit properly, and a small ulcer can progress to infection or worse. A used shoe molded to someone else’s foot geometry is an especially poor choice for anyone managing diabetic foot risk, because the pressure points will be in all the wrong places.
How to Clean Used Shoes Before Wearing Them
The good news is that most microbial risk can be substantially reduced with straightforward cleaning. Here’s what actually works:
- UV-C sanitizers: Ultraviolet shoe sanitizers are effective at reducing fungal burden inside shoes, and even a single treatment cycle produces a meaningful reduction in fungal colonization.11PubMed. Optimization of an infected shoe model for the evaluation of an ultraviolet shoe sanitizer device These devices are widely available and require no chemicals.
- Replace the insole: The insole absorbs the most sweat and harbors the most microorganisms. Pulling it out and replacing it with a fresh one eliminates a large portion of the microbial load and also removes much of the previous wearer’s foot impression.
- Antifungal sprays: Over-the-counter antifungal shoe sprays containing ingredients like tolnaftate or undecylenic acid can help, though as the athletic-shoe sanitization research showed, molds and yeasts are more stubborn than bacteria.
- Thorough drying: Fungi and bacteria need moisture. After cleaning, stuff shoes with newspaper or use a shoe dryer, and store them in a dry, ventilated spot.
- Machine washing: Canvas sneakers and some fabric shoes can go through a gentle cycle with hot water, which addresses both odor and surface contamination. Check the construction first, because glued soles can separate in the wash.
No single cleaning method eliminates every risk, but combining a few of them, especially replacing the insole and using a UV-C device, gets you close to a functionally clean shoe.
What to Inspect Before You Buy
A two-minute inspection at the thrift store or before clicking “buy” online can tell you most of what you need to know. Start with the outsole: hold the shoe at eye level and look at the tread from behind. If the heel is visibly worn down more on one side, the shoe has been heavily used and has adopted a tilt that will change your gait. Press a thumbnail into the midsole; if the foam barely bounces back, the cushioning is mostly spent. Check the interior lining for discoloration, peeling, or persistent odor, all signs of heavy use that cleaning may not fully reverse.
Flex the shoe at the ball of the foot. A shoe that creases sharply or feels overly soft there has lost structural integrity in the forefoot. For leather shoes, look for deep creasing across the vamp, which suggests prolonged wear, versus light surface creasing, which is cosmetic and harmless. Finally, check for any deformation in the heel counter, the stiff cup at the back of the shoe that keeps your heel centered. A collapsed heel counter means the shoe will not support your foot properly no matter how clean it is.
Online purchases are trickier because you cannot perform a physical inspection. Look for seller photos taken from the back, showing the heel wear, and from the side, showing midsole compression. Ask for close-ups of the insole. Platforms that allow returns give you a safety net that makes the gamble more reasonable.
Why Shoes Trigger More Disgust Than Other Secondhand Items
If the idea of wearing someone else’s shoes makes your skin crawl more than wearing their sweater, you are not alone, and the reaction is not entirely irrational. A study on secondhand product perceptions found that consumers were least positive about purchasing used shoes compared to other clothing, with significantly higher concerns about foul smell and hygiene.12Resources, Conservation and Recycling. Walk a mile in someone’s sweaty second-hand shoes: Differences in motivations and barriers for second-hand products The researchers noted that shoes come into direct contact with feet, which sweat and harbor bacteria, and that footwear molds to the shape of the previous wearer’s feet, raising additional concerns about comfort.
There is also a psychological dimension rooted in what researchers call the “law of contagion,” the intuition that an object retains the essence of someone who has touched it. Experimental research found that as the degree of skin contact with a secondhand item increases, perceived contamination rises and purchase likelihood drops. Structural changes to the item, which act as a kind of symbolic purification, can reduce that perceived contamination and make buyers more willing to purchase.13Kafkas Üniversitesi İktisadi ve İdari Bilimler Fakültesi Dergisi. IS PREVIOUS TOUCH ON SECOND-HAND CLOTHES PERCEIVED CONTAGIOUS? AN EXPERIMENTAL RESEARCH In practical terms, this means that swapping out the insole, giving the shoes a visible cleaning, or even relacing them with new laces can make a used pair feel more psychologically “yours,” regardless of whether those steps are microbiologically necessary.
Which Types of Used Shoes Are the Best and Worst Bets
Not all secondhand shoes carry the same level of risk. The combination of how much the shoe was worn, what it was worn for, and how it was constructed determines whether it is a smart buy or a liability.
- Best bets: Dress shoes, heels, and formal footwear that people wear only occasionally. Leather-soled shoes that show minimal tread wear. Kids’ shoes that were outgrown quickly. Boots with replaceable insoles and sturdy construction.
- Acceptable with caution: Casual sneakers and walking shoes with light wear. Sandals and open-toe shoes, which dry out faster and harbor fewer organisms. Any shoe where the midsole still has bounce and the heel counter is firm.
- Poor bets: Running shoes and athletic trainers, especially from serious runners. Any shoe with a visibly collapsed heel, a heavily compressed midsole, or a tilted outsole. Shoes with fabric linings that are stained or smell musty despite airing out. Work boots from industrial settings.
The Environmental Case for Buying Secondhand
The sustainability argument for used shoes is substantial. Shoes are among the most commonly reused items in secondhand markets, and research analyzing secondhand shops found that most reused items, including shoes, were in good enough condition to replace new purchases, conserving the resources that would have gone into manufacturing.14Resources, Conservation and Recycling. Opportunities for circular economy in waste reuse: Insights from social media data mining A single pair of running shoes requires dozens of raw materials, considerable water and energy, and generates a meaningful carbon footprint during production and shipping. Extending the usable life of a shoe by even one additional owner avoids all of that.
The tension between hygiene concerns and environmental benefits is real, and there is no reason it has to be an all-or-nothing choice. Buying used formal shoes you will wear a few times a year while buying new athletic shoes you will run hundreds of miles in is a perfectly rational split. The shoes most worth buying secondhand happen to be the ones with the lowest health risk, and the shoes with the highest risk happen to be the ones worth buying new. Following that pattern gets you most of the environmental benefit with very little of the downside.