Millions of people wear contact lenses safely every day. But contact lenses are medical devices that sit directly on the surface of the eye, and how they are worn, handled, cleaned, and stored can influence the risk of infection.
The most serious contact-lens-associated infection studied in the research is microbial keratitis, an infection of the cornea caused by microorganisms such as bacteria, fungi, or protozoa.
Fortunately, microbial keratitis is uncommon in absolute terms.
But when it does occur, it can progress rapidly and may cause corneal scarring, require surgery, or lead to permanent vision loss.
Decades of epidemiologic and microbiological research point to a consistent conclusion:
Contact lens infection risk is influenced not just by the lens itself, but by what happens to that lens before, during, and after wear.
Some habits—especially sleeping in lenses, exposing them to water, poor hand hygiene, improper storage-case care, and inconsistent cleaning—have repeatedly been associated with higher risk.
Here is what the research actually shows.
How Common Are Contact Lens Infections?
There is no single reliable global infection rate that applies to every contact lens wearer.
Studies differ by:
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country
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climate
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lens type
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wear schedule
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study period
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patient population
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definition of microbial keratitis
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whether researchers count all infections or only severe cases
For that reason, older incidence studies should not be treated as exact predictions for an individual contact lens wearer today.
They are still useful, however, for understanding patterns.
A major Australian population study published in 2008 estimated annual microbial keratitis incidence at approximately:
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1.2 per 10,000 daily-wear rigid gas-permeable lens users
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1.9 per 10,000 daily-wear soft lens users
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2.0 per 10,000 daily-disposable users
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19.5 per 10,000 overnight soft lens users
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25.4 per 10,000 overnight silicone-hydrogel lens users
Those numbers came from one population and one period, so they should not be interpreted as universal modern rates.
The important pattern was the large difference between daytime wear and overnight wear.
Similar research from the Netherlands and Hong Kong also found substantially higher microbial keratitis incidence with extended or overnight soft-lens wear than with daily wear.
Sleeping in Contact Lenses Is One of the Strongest Risk Factors
Of all the modifiable behaviors studied, sleeping in contact lenses is one of the most consistent risk factors for infection.
CDC summarizes the epidemiologic evidence as showing approximately a six- to eightfold increase in contact-lens-related eye infection risk associated with sleeping in lenses.
That includes people who only occasionally sleep in them.
Why?
Contact lens wear already changes the environment at the surface of the eye. Keeping a lens on during sleep extends that exposure while the eye is closed and creates conditions that can make the cornea more vulnerable to microbial infection.
This is why cleaning a lens perfectly the next morning does not erase the risk created by sleeping in it overnight.
Some lenses are specifically approved for extended wear, but approval does not mean overnight wear carries the same risk as daytime-only wear.
For ordinary daily-wear lenses, removal before sleep remains one of the most important safety habits.
Hand Hygiene Matters Even With Daily Disposable Lenses
It is easy to assume that daily disposable lenses solve most hygiene problems.
They do remove several important steps.
A properly used daily disposable does not require:
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overnight storage
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a storage case
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repeated disinfection
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reused lens-care solution
But your fingers still touch the lens before it touches your eye.
In a prospective study involving 963 daily-disposable contact lens wearers, less frequent handwashing was independently associated with microbial keratitis.
Overnight wear was also an independent risk factor.
So even with a fresh lens every day, good hygiene still matters.
Before inserting or removing contact lenses:
Wash your hands with soap and water and dry them thoroughly.
Drying is important too. Handling lenses with wet hands can introduce waterborne microorganisms into the lens-care system.
Water and Contact Lenses Are a Risky Combination
One of the strongest hygiene messages from CDC, FDA, and WHO guidance is simple:
Keep contact lenses away from water.
That includes:
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tap water
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bottled water
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distilled water
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swimming pools
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hot tubs
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lakes
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oceans
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shower water
Water that is safe to drink is not sterile.
Of particular concern is Acanthamoeba, a free-living microorganism found in water and soil.
Acanthamoeba can cause Acanthamoeba keratitis, a rare but potentially severe corneal infection that is strongly associated with contact lens wear.
WHO's recent drinking-water guidance specifically highlights the risk of eye infection when nonsterile water is used to clean or store contact lenses.
Research also supports the connection between water exposure and contamination.
In one study of 165 soft-lens wearers, water-related behaviors were common, and water exposure was associated with greater lens-case contamination. Showering while wearing contacts was associated with greater case bioburden, while handling lenses with wet hands was associated with higher case endotoxin.
That does not mean every shower in contact lenses will cause an infection.
It means water creates a preventable route through which environmental microorganisms can enter the contact lens system.
Why Acanthamoeba Deserves Special Attention
Acanthamoeba is different from ordinary bacterial contamination.
It can form a hardy cyst stage that is unusually resistant to environmental stress and can be difficult for some disinfecting systems to eliminate.
Research has also found meaningful differences in how individual contact lens solutions perform against Acanthamoeba.
A U.S. outbreak investigation published in 2009 found a strong association between Acanthamoeba keratitis and a particular multipurpose contact lens solution.
The unopened solution itself was not found to be contaminated. Instead, researchers raised concerns about insufficient anti-Acanthamoeba activity under real-world use conditions.
That history provides an important lesson:
Safe contact lens care is not simply a matter of using “some contact solution.”
The specific product, lens compatibility, care process, and wearer behavior all matter.
Your Contact Lens Case Can Become a Microbial Reservoir
A storage case may look clean while still containing microorganisms.
One 2010 study of asymptomatic contact lens wearers found microbial contamination in 37 of 64 cases—about 58%.
Older microbiological research detected:
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bacteria in 77% of sampled cases
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fungi in 24%
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Acanthamoeba in 8%
Those are contamination rates, not infection rates.
Most contaminated cases do not cause keratitis.
But the findings demonstrate that a storage case is not just passive packaging. It can become a reservoir from which microorganisms are repeatedly reintroduced to the lens.
That is why case hygiene is part of contact lens hygiene.
For standard reusable-lens cases, current guidance recommends:
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Discard used solution completely.
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Rub and rinse the case with fresh contact lens disinfecting solution rather than water.
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Remove excess liquid.
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Allow the case to dry properly.
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Replace the case regularly.
FDA recommends replacing the case approximately every three months or as directed by your eye-care professional.
What Is a Biofilm?
Microorganisms do not always remain as isolated cells floating freely in solution.
Once they attach to a surface such as a contact lens case, they can form a biofilm.
A biofilm is an organized microbial community embedded in a protective extracellular matrix.
Biofilm organisms can behave differently from free-floating microorganisms and may become harder to remove or kill.
This helps explain why simply pouring new disinfecting solution into a contaminated case is not always enough.
Mechanical cleaning and proper drying matter because they help physically disrupt and remove contamination from the surface.
Protein and Lipid Deposits Can Change the Lens Surface
Microorganisms are not the only things that accumulate on reusable contact lenses.
The tear film contains:
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proteins
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lipids
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salts
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mucins
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other biological molecules
Some of these materials deposit on or within contact lens materials during wear.
The relationship between deposits and infection is complex.
It would be too simplistic to say that “protein buildup feeds bacteria.”
Some tear proteins can actually have antimicrobial properties, while the effects of deposits vary with the protein, lens material, degree of denaturation, and other conditions.
However, laboratory studies show that lens deposition can change the way bacteria interact with the contact lens surface.
A 2024 laboratory investigation found that certain deposit conditions could increase bacterial adhesion and biofilm formation and alter the effectiveness of disinfection systems.
This supports regular cleaning of reusable lenses—but it does not prove that one visible protein deposit directly causes infection.
Why Rub-and-Rinse Cleaning Still Matters
Modern contact lens solutions can disinfect lenses chemically.
But mechanical cleaning still plays an important role.
In a 2011 study, researchers tested different multipurpose contact lens solution regimens against microorganisms.
The greatest microbial removal occurred when rubbing and rinsing were performed before disinfection.
A no-rub/no-rinse approach left significantly more microorganisms behind.
The logic is straightforward:
Rubbing loosens organisms and deposits.
Rinsing carries loosened material away.
Disinfection acts on microorganisms that remain.
Each step performs a different job.
That is why current CDC guidance continues to recommend rubbing and rinsing reusable lenses with the appropriate disinfecting solution every time they are removed.
Cleaning and Disinfection Are Different
These two terms are often used interchangeably, but they describe different processes.
Cleaning
Cleaning removes:
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deposits
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debris
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mucus
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lipids
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proteins
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some microorganisms
Disinfection
Disinfection uses an antimicrobial system to reduce harmful microorganisms that remain.
This distinction explains why sterile saline is not a disinfectant.
Saline can rinse a lens when appropriate, but it does not provide the antimicrobial disinfection required before reusable lenses are worn again.
A lens can look perfectly clean while still carrying viable microorganisms.
Why Fresh Contact Lens Solution Matters
Used solution should be discarded after every storage cycle.
Do not pour fresh solution on top of old solution left in the case.
This practice is known as “topping off.”
Old solution has already been exposed to:
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the lens
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the case
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microorganisms
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deposits
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environmental contamination
Adding a little new disinfectant does not transform that mixture back into a fresh disinfection system.
CDC and FDA therefore recommend using completely fresh solution every time reusable lenses are stored.
Multipurpose Solution vs. Hydrogen Peroxide
Reusable soft lenses are commonly disinfected using either:
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a multipurpose solution
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a hydrogen-peroxide system
Both can form part of an effective care regimen when properly selected and used.
Multipurpose solutions
Multipurpose solutions can combine:
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cleaning
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rinsing
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disinfection
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storage
They are convenient, but not every formulation performs identically.
Antimicrobial performance can differ depending on:
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active ingredients
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microorganism
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lens material
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deposits
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contact time
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actual user technique
Historical outbreaks involving individual multipurpose solutions demonstrate why performance should be evaluated at the product level rather than assuming that every solution in a category behaves identically.
Hydrogen peroxide systems
Hydrogen peroxide provides strong oxidative disinfection and is generally preservative-free after proper neutralization.
That can make it useful for some wearers who are sensitive to preservatives in multipurpose solutions.
However, hydrogen peroxide introduces its own critical safety requirement:
It must be fully neutralized before the lens touches the eye.
The dedicated case supplied with the system is not optional.
Unneutralized hydrogen peroxide can cause intense burning, irritation, and corneal injury.
Research also shows that not every peroxide formulation performs identically against resistant organisms such as Acanthamoeba cysts.
So the evidence does not support a simple statement that one broad solution category is always safest.
The more useful rule is:
Use a lens-compatible system recommended for you and follow its instructions exactly.
What Research Says About Daily Disposable Lenses
Daily disposable lenses offer a meaningful hygiene advantage because they eliminate the repeated storage-and-disinfection cycle.
Used properly, there is:
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no old lens to clean
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no storage case
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no reused solution
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no repeated deposit accumulation across multiple days
But daily disposables are not infection-proof.
In the Australian population study, microbial keratitis incidence for daily disposables was estimated at approximately 2.0 per 10,000 wearers per year, very similar to the 1.9 per 10,000 estimate for daily-wear soft lenses overall.
That does not mean daily disposables have no hygiene benefit.
Rather, infection depends on multiple pathways.
Daily disposables remove case- and solution-related risks but do not eliminate:
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contaminated hands
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water exposure
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overnight wear
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excessive wear time
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ocular-surface susceptibility
Their benefit also depends on actually treating them as disposable.
A daily disposable that is stored and reused is no longer being used according to its intended single-use design.
What About Ortho-K?
Orthokeratology, or Ortho-K, requires separate consideration.
Ortho-K lenses are specially fitted rigid gas-permeable lenses intentionally worn overnight to temporarily reshape the cornea.
Because overnight wear is part of the treatment, the usual recommendation to remove ordinary contacts before sleep cannot simply be applied.
Recent data suggest that microbial keratitis remains uncommon but possible.
A 2025 Japanese multicenter study involving 1,438 patients and 7,415 patient-years of wear identified four microbial keratitis cases, corresponding to approximately 5.4 cases per 10,000 patient-years.
An earlier U.S. analysis estimated approximately 7.7 cases per 10,000 patient-years.
Because relatively few infections occurred, the confidence intervals around these estimates are broad.
The appropriate conclusion is not that Ortho-K is inherently unsafe.
It is that meticulous hygiene matters particularly for a reusable lens that is deliberately worn during sleep.
Ortho-K users should follow their prescribed RGP-compatible care system, clean and disinfect lenses after morning removal, avoid water exposure, maintain the lens case carefully, and keep regular follow-up appointments.
How Poor Hygiene Can Turn Contamination Into Infection
A contaminated lens does not automatically cause microbial keratitis.
Several things generally have to go wrong.
A simplified pathway looks like this:
Microorganisms reach the lens or case → survive cleaning or disinfection → attach or persist → return to the eye → encounter a susceptible corneal surface → infection develops
Good hygiene works by interrupting that chain at multiple points.
Handwashing reduces microbial transfer.
Rub-and-rinse cleaning lowers surface contamination.
Disinfection kills many remaining microorganisms.
Fresh solution avoids recycling contaminated liquid.
Case cleaning removes another reservoir.
Water avoidance prevents exposure to environmental organisms.
Removing lenses before sleep reduces a major host-related risk factor.
No single step makes infection impossible.
Together, however, they reduce several preventable routes by which microorganisms can reach and persist on the eye.
What the Strongest Evidence Supports
When decades of epidemiology, microbiology, outbreak investigations, laboratory studies, and current clinical guidance are considered together, a small number of behaviors stand out.
1. Do not routinely sleep in ordinary daily-wear lenses
Overnight wear is one of the strongest and most consistent modifiable risk factors.
2. Keep lenses away from water
Do not rinse or store contacts in water, and remove them before swimming or showering whenever possible.
3. Wash and completely dry your hands
This matters even if you wear a fresh daily disposable every morning.
4. Rub and rinse reusable lenses
Mechanical cleaning improves microbial and deposit removal.
5. Use fresh disinfecting solution every time
Never top off yesterday's solution.
6. Complete the full disinfection period
Do not shorten the prescribed soak or neutralization time.
7. Treat the storage case as part of the hygiene system
Clean, dry, and replace it regularly.
8. Follow the replacement schedule
A reusable lens should not be worn indefinitely simply because it still feels comfortable.
What the Research Does Not Prove
Responsible contact lens advice also requires acknowledging uncertainty.
The evidence does not show that:
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one missed cleaning step guarantees an infection
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perfect hygiene reduces risk to zero
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daily disposables eliminate microbial keratitis
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every hydrogen-peroxide system is superior to every multipurpose solution
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all protein deposits are harmful
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enzymatic cleaning has been proven to prevent keratitis
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one historical infection rate applies to every wearer today
Many hygiene studies measure intermediate outcomes such as:
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contamination
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microbial load
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endotoxin
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behavior change
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biofilm removal
These are useful, but they are not the same as directly demonstrating fewer cases of microbial keratitis.
Because microbial keratitis is relatively rare, enormous randomized trials would be required to test every hygiene intervention using infection itself as the endpoint.
Modern recommendations therefore rely on the convergence of multiple types of evidence.
Warning Signs Contact Lens Wearers Should Not Ignore
Good hygiene reduces risk, but contact lens wearers should also recognize symptoms that may indicate something more serious than ordinary dryness or irritation.
Remove your lenses and seek prompt eye-care advice if you develop:
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significant or increasing eye pain
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pronounced redness
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light sensitivity
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unusual discharge
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sudden blurred vision
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reduced vision
Do not simply disinfect the lens and put it back in.
FDA warns that contact-lens-associated corneal infections and ulcers can progress quickly, and early evaluation can be important.
Frequently Asked Questions
What causes most contact lens infections?
There is no single cause. Research repeatedly implicates overnight wear, contaminated hands, water exposure, poor storage-case hygiene, inadequate cleaning and disinfection, and other handling behaviors.
How much does sleeping in contacts increase infection risk?
CDC summarizes studies as showing approximately a six- to eightfold increase in contact-lens-related eye infection risk associated with sleeping in contacts. Individual risk varies by lens, wearer, and study population.
Should reusable contacts be cleaned every day?
If they are removed every day and will be worn again, yes. Reusable lenses should be cleaned and disinfected every time they are removed before reuse.
Are daily disposables safer?
They eliminate routine storage, disinfection, and case contamination when used correctly, which is a meaningful hygiene advantage. But they do not eliminate infection risk from hands, water exposure, or sleeping in lenses.
Do I really have to rub my contact lenses?
For compatible reusable lens-care systems, current CDC guidance recommends rubbing and rinsing. Experimental evidence shows that mechanical rubbing improves removal of microorganisms.
Can I rinse my contacts with tap water?
No. FDA, CDC, and WHO guidance recommends keeping contacts away from nonsterile water because of environmental organisms including Acanthamoeba.
Is saline enough to disinfect lenses?
No. Sterile saline may rinse a lens, but it does not disinfect it.
Is hydrogen peroxide safer than multipurpose solution?
Not universally. Both can be effective when appropriately chosen and correctly used. Hydrogen peroxide must be completely neutralized in its dedicated system before the lens touches the eye.
How often should I clean my contact lens case?
After every use. Empty the old solution, clean and rinse the case with appropriate fresh contact lens solution rather than water, and allow it to dry properly.
How often should I replace my lens case?
FDA recommends replacing it approximately every three months or according to your eye-care professional's instructions.
The Bottom Line
Contact lens infections are uncommon for most wearers, but they are not random.
Research consistently shows that the way lenses are worn and cared for influences risk.
The strongest evidence points toward a few simple habits:
wash and dry your hands, keep lenses away from water, rub and rinse reusable lenses, use fresh disinfectant, complete the full soak time, keep the case clean and dry, replace lenses and cases on schedule, and avoid sleeping in lenses unless overnight wear is specifically prescribed.
No care routine can make contact lens wear completely risk-free.
What good hygiene can do is repeatedly interrupt the pathways that allow microorganisms to reach the lens, survive, persist, and eventually infect the cornea.
That is why contact lens hygiene is not simply about comfort or keeping a lens looking clean.
It is an important part of protecting the health of the eye.
Sources
Centers for Disease Control and Prevention — Preventing Eye Infections When Wearing Contacts
https://www.cdc.gov/contact-lenses/prevention/index.html
Centers for Disease Control and Prevention — Cleaning, Disinfecting, and Storing Contact Lenses
https://www.cdc.gov/contact-lenses/about/about-cleaning-disinfecting-and-storing-contact-lenses.html
CDC / MMWR — Corneal Infections Associated with Sleeping in Contact Lenses
https://www.cdc.gov/mmwr/volumes/67/wr/mm6732a2.htm
U.S. Food and Drug Administration — Contact Lens Solutions and Products
https://www.fda.gov/medical-devices/contact-lenses/contact-lens-solutions-and-products
U.S. Food and Drug Administration — Safe Use of Hydrogen Peroxide Solution
https://www.fda.gov/consumers/consumer-updates/contact-lenses-safe-use-hydrogen-peroxide-solution
World Health Organization — Acanthamoeba: Background Document for the WHO Guidelines for Drinking-water Quality
https://iris.who.int/items/625539f3-9805-4ff9-b268-58b952763d93
American Academy of Ophthalmology — Eye Infections From Contact Lenses
https://www.aao.org/eye-health/diseases/contact-lens-related-eye-infections
American Academy of Ophthalmology — Bacterial Keratitis Preferred Practice Pattern
https://www.aao.org/education/preferred-practice-pattern/bacterial-keratitis-ppp-2023
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