Pick up a dusty old lens from a flea market, an estate sale, or even your own forgotten storage bin, and you might notice something strange glinting beneath the surface of the front element: delicate white threads, odd patterns like spiderwebs or frost creeping across the inside of the glass. That eerie substance is lens fungus — an unwelcome guest in the world of photography that quietly invades optical systems, thrives in darkness and moisture, and, if left untreated, can cause permanent and costly damage to your equipment.
Lens fungus is not just an aesthetic problem. While it may start invisibly, it can grow into something that degrades image quality, lowers lens resale value, and sometimes renders optics beyond repair. It’s especially concerning for photographers who own vintage manual-focus lenses or those who store their gear in high-humidity environments. The issue is more common than many beginners expect, and the threat it poses is often misunderstood or dismissed as overblown—until it’s too late.
This guide provides a comprehensive overview of lens fungus, including its characteristics, potential spread to other lenses, and methods for identification, prevention, and management. Whether you’re a hobbyist with a modest kit or a professional managing thousands of dollars’ worth of glass, understanding this quiet, insidious threat is crucial to maintaining the longevity and integrity of your photographic tools.
What Is Lens Fungus?
Lens fungus refers to microbial growth — typically mold — that develops inside photographic lenses. It’s not a single species but a general term for several types of fungi that thrive in environments containing three ingredients: moisture, darkness, and organic material. Inside lenses, this “organic material” can be dust particles, grease from lubricants, or even trace amounts of skin oil. When a lens is stored in a humid environment and not regularly exposed to light, it can become an ideal breeding ground for destructive fungi.
Fungi reproduce by releasing spores — microscopic airborne particles that exist virtually everywhere. These spores are almost impossible to avoid; they’re present in most indoor and outdoor environments. The issue isn’t whether spores are there (they are), but whether the conditions allow them to activate. Inside a lens, spores can remain dormant for years until the relative humidity (RH) rises above approximately 60%, at which point they germinate and begin to spread filament-like structures called hyphae.
The patterns created by these fungal hyphae often look like cobwebs, snowflakes, or branching veins. Early infestations may be challenging to see without shining a flashlight directly through the lens elements. But as the colony grows, it can begin to cover wider areas of the glass and eventually become visible through the front or rear elements during regular use.
Lens fungus doesn’t just sit harmlessly on the surface of the glass. Some types secrete organic acids — such as hydrofluoric acid — that can slowly etch lens coatings and even damage the underlying glass. Magnesium fluoride, a common anti-reflective coating, is particularly susceptible. Once this etching occurs, the damage is permanent. Even if the fungal growth is later cleaned off, the optical quality of the lens will never fully recover if the coatings have been dissolved or the glass surface has been pitted.
Fungal outbreaks most often appear in older lenses with less advanced weather sealing, though modern lenses are not immune. They are commonly found in lenses that have been stored in closets, attics, basements, or camera bags that rarely see the light of day. The internal air in these spaces may be stagnant and humid, creating the perfect environment for growth. Lenses left unused for long periods are also more vulnerable because the internal environment doesn’t benefit from air circulation or light exposure.
Does Lens Fungus Affect Image Quality?
A common myth among beginner photographers is that “a little fungus doesn’t affect anything.” While it’s true that a light growth near the edge of a front element may not have a noticeable impact on image sharpness, this is only true in the early stages. As the fungal colony grows, the effect on image quality becomes more severe — and sometimes irreversible, particularly once the fungus begins to etch the lens’s coating.
Even minor fungal growth can scatter light as it passes through the lens elements. This leads to a reduction in contrast and an increase in flare. Backlit subjects, in particular, can show signs of blooming or ghosting, as the filaments inside the lens refract light in unpredictable ways. Photographers may notice that their images appear softer, more washed out, or lacking in depth, especially in high-contrast scenes.
Independent tests from photography forums and optical labs have shown that once a fungal colony covers more than 15–20% of the lens element surface, image degradation becomes statistically measurable. Color fidelity suffers, blacks become gray, and micro-contrast — the fine tonal differentiation between areas of high frequency that gives images texture — drops off dramatically.
Fungus can also create a general “haze” inside the lens, similar to what happens with internal fogging or decaying lubricants. This haze, although subtle at first, reduces the transmission of light through the glass, resulting in lower brightness in the viewfinder and sensor. In extreme cases, an infected lens may appear permanently foggy or misty, even in bright light, due to widespread internal scattering.
However, the most serious consequence of lens fungus is not what the living organism does, but what it leaves behind. As mentioned earlier, some species of fungi release acidic byproducts as they feed on organic material or optical glue. These byproducts can etch anti-reflective coatings or even damage the physical surface of glass elements. Once the coating is etched, it cannot be repaired without professional re-coating — something that is rarely economical for most consumer lenses.
In such cases, even professional cleaning can only remove the biological remnants of the fungus. The etched marks, like tiny, frosted spots on the glass, will continue to scatter light, permanently degrading the image. The result is a lens that may still work mechanically but has suffered a permanent optical downgrade, reflected in both its performance and its resale value.
Can Lens Fungus Spread from Lens to Lens?
A frequently asked question among photographers, especially those who buy and sell used lenses, is whether lens fungus can “infect” other lenses in their collection. The short answer is: not directly, but yes, under the right conditions.
Fungal spores are airborne and omnipresent. Every lens you own has already been exposed to spores at some point. What makes a lens susceptible to fungal growth isn’t the presence of spores themselves, but the conditions inside and around the lens — specifically moisture and darkness. This means that simply storing a fungus-infected lens in the same cabinet as your other lenses won’t automatically lead to a fungal outbreak across your gear. However, if that cabinet has high humidity and poor ventilation, then multiple lenses may begin showing signs of fungus over time — not because the first one “infected” the others, but because the shared environment allowed latent spores in all of them to flourish.
That said, physical cross-contamination is possible. If you handle a fungus-infected lens and then touch another lens without washing your hands, or if you reuse the same cleaning cloths, brushes, or caps, you might transfer small spores or fragments of hyphae to other gear. In this sense, it is wise to treat lenses with visible fungus as potential biohazards until they’re properly cleaned or isolated.
For this reason, many photographers isolate infected lenses in airtight plastic bags with desiccant packs until they can be examined or repaired. Some go further, quarantining the lens in a separate room and labeling it clearly to avoid mix-ups. If you must inspect a questionable lens, do it in a well-ventilated area away from your main gear storage, and use disposable gloves or alcohol-based hand sanitizer afterward.
To summarize: fungus doesn’t leap between lenses like a contagious disease, but it can exploit shared conditions or careless handling. Proper humidity control, gear hygiene, and sensible storage practices are your best defense against letting one bad lens lead to a full-blown outbreak.
What Does Lens Fungus Look Like?
If you’ve never seen lens fungus up close, it’s easy to mistake it for internal dust, haze, or even lens separation. However, once you recognize the signs, it becomes easier to identify them. Most fungal growth begins subtly, often as translucent threads that are barely visible without direct light. To inspect a lens for fungus, shine a bright LED flashlight through the rear element and look at the front, and vice versa. This backlighting will reveal any filaments, patches, or haze inside. Note: it can also reveal a lot of imperfections, such as dust, that are extremely common (even in new lenses), and you shouldn’t worry too much about.
Common fungal patterns include:
- Cobwebs or spiderweb filaments: Thin, branching lines that radiate from a point outward. These often resemble frost or snowflakes and are usually seen on or near the edges of front or rear elements.
- Circular colonies: Some fungi form rounded, slightly fuzzy spots that expand concentrically. These can resemble dried water droplets or oil smudges but won’t wipe off.
- Hazy patches: A cloudy area in the center or edge of a lens, sometimes misidentified as fog or balsam separation. If it has a feathery texture, it’s likely fungal.
- Etch marks: If the fungus has died or been partially cleaned, it may leave behind ghostly white rings or patches—these are permanent scars from acid secreted by the organism.
It’s vital to differentiate fungus from common issues like balsam separation (the deterioration of the cement between lens elements), which appears as rainbow discoloration or cracks near the edge, or internal dust, which looks like small dark specks. Only fungal filaments show the delicate, root-like growth structure that fans out across a surface. Photos of infected lenses under magnification reveal the beautiful but destructive nature of fungal colonies — like tiny ice crystals spreading over glass.
How to Prevent Lens Fungus
The best way to deal with lens fungus is to prevent it from developing in the first place. Prevention is about the environment, storage practices, and awareness of how fungus grows.
Control Humidity
The number one factor in fungal development is humidity. Once the relative humidity (RH) climbs above 60%, spores can germinate. That means storing your gear in a damp basement or a closed cabinet in a tropical climate is inviting trouble. The ideal RH for lens storage is between 30% and 50%.
Use a dry cabinet or an airtight container with desiccant packets. Commercial dry cabinets have electronic humidity controls and are ideal for serious collectors or professionals — personally, I use Ruggard cabinets, which are frequently on sale at B&H Photo and come in a huge variety of sizes and shapes to fit your needs. Budget alternatives include plastic storage boxes with a tight seal and silica gel packs, which can be recharged in an oven or replaced regularly.
Note that a dry cabinet is not strictly necessary if you have air conditioning (air conditioning removes humidity). But, if you live in a humid climate, check the RH regularly using a hygrometer. Don’t rely on air conditioning alone to regulate it — air conditioners remove moisture, but only when running, and rooms can rehumidify quickly when they’re off.
Use and Air Your Lenses
Lenses stored and unused for long periods are more likely to grow fungus. That’s because the inside of a lens stays dark and unventilated. Simply using your lenses helps reduce the risk. The motion of focusing and zooming pushes and pulls air through the lens barrel, allowing moisture to dry out and preventing stagnation.
Every few weeks, remove your lenses from storage and expose them to natural light — indirect sunlight works best. UV light helps inhibit fungal growth, though too much direct sunlight can heat the lens excessively and damage lubricants. A half-hour in the shade or morning light is usually enough.
Avoid Condensation
Sudden changes in temperature and humidity can cause condensation inside a lens. For example, moving from an air-conditioned building into hot, humid air — such as walking from a hotel into the rainforest — will cause moisture to form on and inside cold lenses.
To avoid this, keep gear in a sealed zip-lock bag when moving between environments. Let it gradually warm up before opening the bag. After a humid shoot, store lenses with silica gel to absorb any residual moisture.
Clean External Surfaces
Fungus feeds on dust, oils, and lubricants—so a clean lens is less inviting. Wipe down the external glass with a microfiber cloth and a blower bulb. Clean rear caps, front caps, and pouches periodically, especially if you’ve used them in damp conditions. Always let gear dry thoroughly before storage.
Consider Desiccant Caps and Specialized Storage
Some photographers use accessories like BRNO dri+Caps, which are body and rear lens caps that contain moisture-absorbing gel packs. These are useful when traveling in unpredictable weather or when you don’t have a dry box available.
How to Deal With Lens Fungus
Sometimes, despite best efforts, fungus shows up. Whether to clean or replace the lens depends on how far the fungus has spread and what damage has been done.
Step 1: Assess the Severity
Inspect the lens under a flashlight. If the fungal growth is minor—small patches near the edge, no visible etching—it may be treatable with a DIY approach. If the fungus is dense, affects multiple internal surfaces, or if you see etching, haze between elements, or circular acid marks, professional help is likely needed.
If the lens is expensive or rare, it’s worth contacting a repair shop for a quote. For cheap vintage lenses, the cost of cleaning may exceed the value of the lens.
Step 2: DIY Cleaning (For Minor Cases)
Disclaimer: Disassembling lenses carries the risk of damage or misalignment. Proceed only if you’re confident in your mechanical skills. Refer to this article for even more information.
Kill the fungus first: Place the lens in indirect sunlight or use a UV sterilization box. This step doesn’t remove the fungus, but it helps sterilize it and prevent further growth.
Clean accessible surfaces: Remove the front name ring or rear element group using appropriate tools (not knives). Using lint-free pads (such as Pec-Pads), gently wipe the affected area with a mixture of hydrogen peroxide and ammonia (the Edwal formula), or use diluted vinegar (5%) and distilled water.
Be sure to use minimal fluid and avoid getting liquid inside the lens barrel. Allow everything to air dry before reassembly.
Note: Never use high-proof isopropyl alcohol on vintage coatings, as it can cloud or dissolve them (learned this the hard way many years back).
Step 3: Professional Cleaning
If fungus is trapped between glued elements or behind complex assemblies, professional service is your best option. Technicians can fully disassemble the lens, clean each component with antifungal agents, and reassemble and calibrate the optics. Costs vary—simple primes may cost $80–150, while zooms or lenses with complex element groups can run $300+.
If there’s etching, professionals can remove the fungus but not the damage. In extreme cases, replacement of elements or coatings may be possible, but this is often prohibitively expensive.
Step 4: Isolate and Monitor
If you decide not to clean a lens—or can’t—seal it in a ziplock bag with desiccant to prevent it from affecting nearby gear. Label it and check it periodically to ensure the fungus isn’t spreading or worsening.
Protect Your Lenses!
Lens fungus is one of the most misunderstood and underestimated threats to camera gear. It doesn’t make dramatic entrances or cause instant failure—it creeps in slowly, feeds silently, and often goes unnoticed until it’s too late. While most lenses harbor dormant fungal spores, it’s the storage environment, not the spores themselves, that determines whether damage will occur.
By controlling humidity, allowing airflow, using your lenses regularly, and maintaining cleanliness, you can reduce the risk of fungal growth dramatically. If fungus does appear, early detection and careful intervention can save your lens. But the longer it’s ignored, the more likely it is to cause irreversible optical damage.
The key takeaway is that your lens is not just a tool—it’s an optical system sensitive to both environmental and biological factors. Treat it with the same care you would give a fine instrument. Store it wisely, use it regularly, and don’t let moisture and darkness invite a tiny organism to destroy what precision engineering has built.
Header photo licensed via Creative Commons, CC-BY-SA 4.0
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