Sunlight can reduce the amount of living fungus in shoes, but it is not a reliable way to fully disinfect them. The ultraviolet radiation and heat in sunlight do have genuine antifungal properties, yet the effect depends heavily on geography, weather, duration of exposure, and how much UV actually reaches the shoe’s interior. A recent review of hygiene practices against dermatophytic fungi concluded that while sun exposure produces “some reduction in fungal load” on textiles, it “may be insufficient for complete disinfection.”1PubMed Central. Hygiene Practices Against Dermatophytic Fungi: A Review of Strategies to Combat Antifungal Resistance The reason lies in a mismatch between what sunlight delivers and what it takes to kill the organisms hiding in your footwear.
What Makes UV Light Antifungal
Ultraviolet radiation damages the DNA and other cellular structures of fungi, interfering with their ability to grow and reproduce. But not all UV wavelengths are equally effective. The UV spectrum is typically divided into three bands: UVA (the longest wavelengths, which make up the vast majority of UV in natural sunlight), UVB (a smaller share, partly filtered by the atmosphere), and UVC (the shortest and most germicidal wavelengths, almost entirely blocked by the ozone layer before reaching the ground).
This distinction matters enormously. Laboratory research on dermatophytes, the group of fungi responsible for athlete’s foot and toenail infections, has found that UVC-range wavelengths are dramatically more effective than UVA. A large data collection comparing antifungal doses across the UV spectrum found that the doses of violet and UVA light needed to achieve the same kill rate as UVC were three to four orders of magnitude higher.2PubMed Central. Fungal photoinactivation doses for UV radiation and visible light–a data collection In practical terms, that means UVA might need roughly a thousand to ten thousand times more energy to do the same job as UVC. Sunlight is overwhelmingly UVA. The wavelengths that are best at killing shoe fungi barely exist in the light that reaches your backyard.
A study testing LED-based UV against Trichophyton rubrum, the single most common cause of athlete’s foot and fungal nail infections, found that exposure at 280 nanometers (in the UVB/UVC boundary range) inhibited growth at a very low energy dose, while exposure at longer wavelengths did not.3PubMed. An investigation into the inhibitory effect of ultraviolet radiation on Trichophyton rubrum The researchers specifically noted that a potential practical application of this finding would be decontaminating shoes, since the effective wavelengths could be generated artificially even though they do not arrive in useful quantities from the sun.
Why Shoes Are Especially Hard to Disinfect With Sunlight
Even if sunlight contained more of the germicidal wavelengths, the physical structure of a shoe works against it. Shoes are enclosed, often made of opaque or thick materials, and the fungi live on interior surfaces: insoles, linings, the toe box. Setting a shoe outside on a sunny day exposes the outer surface to UV, but the inner surfaces where fungi thrive remain largely shaded. UV light travels in straight lines and does not bend around corners or penetrate deeply into fabrics. The toe area of a closed shoe, which stays warm and moist during wear and provides an ideal fungal habitat, is the hardest spot for sunlight to reach.
Heat from sunlight does contribute some antifungal effect. Dermatophytes prefer warm, moist environments and can be stressed by high temperatures and, more importantly, by drying. Leaving shoes in the sun helps evaporate moisture, which makes the environment less hospitable for fungal growth. But there is a difference between slowing fungal growth and actually killing the organisms already embedded in shoe materials. Fungal spores, in particular, are far more resistant to environmental stress than actively growing fungi. They can survive extended periods of drought and moderate heat, then resume growing when conditions improve, such as the next time a sweaty foot slides into the shoe.
The effectiveness of sun exposure also varies enormously by location, season, and weather. In a tropical or subtropical area with intense midday sun, several hours of direct exposure might deliver a meaningful antifungal dose to surfaces that the light can actually reach. In a northern latitude during winter, the UV intensity may be too weak to accomplish much even with a full day outdoors. A review of disinfection strategies noted that effectiveness “varies greatly depending on environmental factors such as sunlight intensity, duration of exposure, and local climate conditions.”1PubMed Central. Hygiene Practices Against Dermatophytic Fungi: A Review of Strategies to Combat Antifungal Resistance
Why Your Shoes Keep Reinfecting Your Feet
People dealing with athlete’s foot or fungal toenails often focus on treating the skin or nails and overlook the shoes. This is a well-recognized problem in dermatology. Shoes provide a warm, dark, moist environment that dermatophytes colonize readily, and fungi can persist in footwear for months. Researchers identified shoes as a reservoir of reinfection as far back as the 1930s, when investigations into recurrent foot ringworm pointed to contaminated shoes as a likely source of persistent problems.4JAMA Dermatology. SHOES: A SOURCE OF REINFECTION IN RINGWORM OF THE FEET
This reinfection cycle is a major reason that foot fungus can feel impossible to get rid of. You might apply an antifungal cream for weeks, clear the infection from your skin, and then put on the same sneakers you were wearing when you caught it. The fungi living in the insole and lining recolonize your feet, and the cycle starts over. Any shoe disinfection strategy, whether sunlight, UV devices, or chemical sprays, exists to break this cycle. The question is not just whether sunlight has some effect on fungi in a general sense, but whether it is effective enough at the specific job of clearing the fungal load inside a contaminated shoe. The evidence suggests it usually is not, at least not on its own.
UV-C Shoe Sanitizing Devices
Because the wavelengths in natural sunlight are not ideal for killing shoe fungi, several manufacturers have developed devices that use artificial UVC light specifically designed to fit inside shoes. These devices emit the short-wavelength UV that is most lethal to dermatophytes but absent from sunlight. You insert them into the shoe, turn them on, and the UV-C radiation reaches the interior surfaces directly.
A study that developed an infected shoe model to test a commercial UV-C sanitizing device found that ultraviolet treatment was effective in reducing the fungal burden in shoes.5PubMed. Optimization of an infected shoe model for the evaluation of an ultraviolet shoe sanitizer device The approach solves two problems at once: it delivers the right wavelength and it delivers it directly to the interior surfaces where fungi live, rather than relying on UV to somehow penetrate from the outside.
These devices typically cost somewhere in the range of $30 to $100, depending on the brand, and treatment cycles run for about 15 to 45 minutes per shoe. For someone dealing with chronic or recurrent foot fungus, they represent a more practical option than relying on the sun. That said, not all devices on the market have been tested in published studies, and the ones that exist vary in power output and design. If you are considering one, look for products that have been evaluated independently rather than relying solely on manufacturer claims.
One limitation of even artificial UV-C is that light still cannot reach every crevice inside a shoe. Areas shielded by folds, stitching, or thick insole padding may not receive a full germicidal dose. This is why many dermatologists recommend combining UV treatment with other strategies rather than relying on any single method.
Chemical Shoe Decontamination
Chemical antifungal sprays and powders offer an alternative or complement to UV-based approaches. These products can penetrate areas that light cannot, seeping into fabric and reaching the underside of insoles. A controlled study tested terbinafine, a common antifungal agent, in spray solution and spray powder form on insoles that had been deliberately colonized with Trichophyton rubrum. A single application of either the spray solution or the powder rendered the insoles completely sterile, with no fungal growth detected at three weeks or six weeks after treatment.6PubMed. A study on the decontamination of insoles colonized by Trichophyton rubrum: effect of terbinafine spray powder 1% and terbinafine spray solution 1%
Other over-the-counter options include sprays containing miconazole, clotrimazole, or tolnaftate, which are the active ingredients in many athlete’s foot sprays and can also be used inside shoes. Some people use household disinfectants like dilute bleach solutions or Lysol, though these have less published evidence for shoe-specific fungal decontamination and may damage certain shoe materials. Antifungal powders have the added benefit of absorbing moisture, which helps keep the shoe environment inhospitable to fungi even after the active ingredient has done its work.
For people actively treating a foot fungal infection, applying an antifungal spray to shoes after each wear is one of the more evidence-supported approaches. It addresses the reinfection reservoir directly and does not depend on sunlight intensity, geographic location, or shoe geometry.
Species and Strains Vary in UV Sensitivity
Not all shoe-relevant fungi respond to UV the same way. Research on Trichophyton species, the primary culprits in foot and nail infections, has shown that different species and even different strains of the same species have markedly different UV sensitivities. A study comparing Trichophyton rubrum and Trichophyton mentagrophytes found that different types of T. rubrum responded differently to UVA, UVB, and UVC radiation, and that T. mentagrophytes showed only slight responsiveness to UVA even at increased doses, though UVB and UVC exposure at higher doses did reduce colony counts.7PubMed Central. The Efficacy of Ultraviolet Irradiation on Trichophyton Species Isolated From Nails The effect depended on both the dose and the type of irradiation.
This variability is relevant because when you have a shoe fungus problem, you do not know exactly which species or strain you are dealing with. A method that works against one type of Trichophyton may be less effective against another. The robustness of fungal spores adds another layer of difficulty, as spores are generally harder to kill than actively growing fungal cells regardless of the method used. This built-in biological variability is one more reason that relying on a single decontamination approach, especially a relatively weak one like natural sunlight, is risky if you are trying to prevent reinfection.
A Practical Approach to Keeping Shoes Fungus-Free
Given the limitations of sunlight alone, a multi-pronged strategy tends to work best. The core principles are reducing moisture, reducing fungal load, and breaking the reinfection cycle.
- Rotate your shoes: Wearing the same pair every day does not give them time to dry out. Alternating between at least two pairs gives each pair a full day or more to air out, which slows fungal growth significantly.
- Remove insoles to dry: After wearing, pull out removable insoles and let them air separately. This speeds drying and exposes more surface area to air circulation.
- Use antifungal spray or powder: Apply an over-the-counter antifungal product inside shoes after wearing, especially if you are actively treating a foot infection. As the terbinafine study showed, even a single application can eliminate fungi on insole surfaces.
- Consider a UV-C device: If you deal with recurrent infections, a UV-C shoe sanitizer provides the germicidal wavelengths that sunlight lacks, delivered directly to the shoe interior.
- Choose breathable materials: Shoes made of mesh, canvas, or perforated materials allow more air circulation and dry faster than solid leather or synthetic uppers. Moisture-wicking socks also help reduce the amount of sweat that reaches the shoe.
- Replace heavily contaminated shoes: If you have had a stubborn fungal infection and worn the same shoes through months of it, decontamination may not reach every colonized fiber. Sometimes the most effective option is to replace old shoes, particularly worn-out athletic shoes with deteriorating insoles.
Sun exposure fits best as a complement to these strategies rather than a standalone approach. If you have no other options available, setting shoes in direct sunlight for several hours is certainly better than leaving them in a dark closet. The UV and heat will slow fungal growth and help dry out moisture. Just do not expect it to sterilize your shoes in the way that a UVC device or an antifungal spray can.
The Moisture Factor Might Matter More Than the UV
One often-overlooked aspect of the “sunlight kills shoe fungus” idea is that some of the benefit people notice from leaving shoes in the sun probably comes from drying rather than from UV-mediated killing. Dermatophytes need moisture to thrive. A shoe that has been sitting in warm, dry, well-ventilated conditions for hours is a less inviting environment for fungi than one that was stuffed in a gym bag. The fungal cells and spores may still be alive, but their ability to grow and cause infection is reduced when the environment turns dry.
This distinction matters because it suggests that on a dry, breezy day with moderate sun, you may get a similar moisture-reduction benefit as on an intensely sunny day. Conversely, in a humid climate where the air itself is damp, even bright sun may not dry shoes effectively. If your primary goal is reducing fungal viability, prioritize drying. Use a fan, stuff shoes with newspaper to absorb moisture, or use a shoe dryer. These approaches remove the moisture that fungi depend on, and they work regardless of whether the sun is out.
Research on athlete sanitization found that sanitizing techniques could meaningfully reduce bacterial counts in footwear, but did not produce a statistically significant decrease in yeast or mold counts, possibly because fungal contamination levels were already low in that particular study.8PubMed Central. Is it possible to sanitize athletes’ shoes? This result hints at a broader reality: fungi, particularly their spores, are stubbornly persistent organisms. Reducing their numbers is achievable; eliminating them entirely from a shoe is harder than most people expect, and typically requires either potent germicidal UV or direct chemical contact rather than ambient environmental exposure.
When Sunlight Might Actually Be Enough
There are scenarios where sun exposure alone might be a reasonable choice. If you do not have an active fungal infection and are simply trying to maintain general shoe hygiene, periodic sun exposure combined with good drying practices is a sensible, low-effort habit. The goal in that case is not sterilization but keeping fungal populations low enough that they do not become a problem. Healthy skin with an intact barrier is quite good at resisting opportunistic fungal colonization even when some spores are present in footwear.
People living in consistently sunny, dry climates also get more benefit from sun exposure than those in northern or humid areas. In parts of the world where intense midday sun is the norm year-round, a few hours of direct sunlight can deliver a substantial UVA and UVB dose. While UVA is far less potent per unit of energy than UVC, enough of it applied long enough does have a measurable effect, especially when combined with the heat-driven drying that accompanies intense sun exposure.
The situations where sunlight falls short are the ones where you really need decontamination to work: chronic or recurrent athlete’s foot, fungal toenail infections, immunocompromised individuals who are more vulnerable to infection, or shared shoes in settings like sports teams. In those cases, the evidence favors more reliable methods. Antifungal sprays directly kill the fungi, UV-C devices deliver the right wavelengths at the right intensity, and drying strategies make the shoe hostile to fungal regrowth. Sunlight alone leaves too much to chance when the stakes are higher than general hygiene maintenance.