Eye infections spread through direct contact with bacteria, viruses, or other microorganisms that reach the surface of your eye or eyelid. The most common routes are touching your eyes with contaminated hands, exposure to infected people’s secretions, improper contact lens care, and contaminated water. Americans make roughly 930,000 doctor visits and 58,000 emergency room visits for eye infections each year.
Touching Your Eyes With Dirty Hands
The single most common way people pick up an eye infection is by transferring germs from their hands to their eyes. Bacteria like Staphylococcus aureus live naturally on your skin and mucous membranes, and viruses like adenovirus (the leading cause of viral pink eye) survive on surfaces for extended periods. Adenovirus has been detected on lockers, shared equipment, and bedding in crowded environments.
When you rub your eyes after touching a contaminated doorknob, phone, or another person’s hand, you deliver those pathogens directly to a warm, moist surface where they thrive. Viral conjunctivitis symptoms can appear anywhere from 12 hours to 12 days after exposure, while bacterial conjunctivitis typically shows up within 24 to 72 hours.
Catching It From Someone Else
Eye infections spread easily between people through several forms of contact. Discharge from an infected person’s eyes or nose carries the pathogen, and you can pick it up by sharing towels, pillowcases, or makeup. Flies can also spread ocular secretions in areas with poor sanitation, which is how trachoma, a chronic and potentially blinding infection, transmits in some parts of the world.
In children, bacterial conjunctivitis is frequently caused by organisms that also live in the nose and throat. These bacteria spread in daycare centers and schools through close contact and shared objects. Newborns can acquire eye infections during delivery if the mother carries certain sexually transmitted bacteria.
Contact Lenses and Improper Care
Contact lenses are one of the biggest risk factors for serious eye infections, particularly bacterial keratitis, an infection of the cornea that can threaten your vision. The two bacteria most commonly responsible are Pseudomonas aeruginosa, found in soil and water, and Staphylococcus aureus from your own skin.
The CDC identifies these specific habits that raise your risk:
- Sleeping in your lenses. Overnight wear creates a warm, low-oxygen environment where bacteria multiply rapidly.
- Rinsing or storing lenses in water. Tap water, bottled water, and even distilled water can harbor microorganisms that disinfecting solution is designed to kill.
- Topping off old solution. Adding fresh solution to used solution dilutes its disinfecting power instead of replacing it.
- Not cleaning your lens case. Biofilm builds up inside the case and becomes a reservoir for bacteria.
- Sharing decorative lenses. Colored or costume lenses passed between people transfer bacteria directly.
Contact lenses also create tiny abrasions on the cornea’s surface. These microscopic scratches give bacteria and parasites an entry point they wouldn’t otherwise have.
Water Exposure
Swimming pools, hot tubs, lakes, and even tap water contain organisms that can infect your eyes. The most concerning is Acanthamoeba, a parasite found in nearly all water sources. If Acanthamoeba reaches an eye that has small surface abrasions, whether from contact lenses, sand, or minor injury, it can cause a severe corneal infection that is notoriously difficult to treat.
This is why swimming with contact lenses in, even while wearing goggles, is risky. The lenses trap contaminated water against the cornea and create the abrasions that let the parasite invade. People with a recent eye scratch or injury who get water in their eyes face a similar risk even without lenses.
Eye Makeup and Cosmetic Products
Your eyelashes naturally carry bacteria. According to the University of Rochester Medical Center, a mascara wand or eyeliner brush becomes contaminated after a single use. Each time you dip the applicator back into the tube, you introduce more bacteria into the product, where they multiply over time.
There are no formal guidelines from regulators, but experts recommend replacing mascara and eyeliner every three to four months. If a product has gone unused for several months, it’s safer to discard it than to assume it’s still clean. Sharing eye makeup is essentially the same as sharing the bacteria living on someone else’s eyelids.
Scratches and Physical Injuries
Any break in the surface of the eye gives bacteria an open door. A corneal abrasion from a fingernail, a tree branch, a piece of debris, or even aggressive eye rubbing compromises the cornea’s natural barrier against infection. What starts as a simple scratch can progress to a full bacterial infection if pathogens enter the wound.
This is why corneal abrasions are taken seriously even when they seem minor. The risk isn’t just the scratch itself but the secondary infection that can follow, especially if the object that caused the scratch was dirty or organic material like soil or plant matter.
Eyelid-Specific Infections
Styes and blepharitis involve infection or inflammation of the eyelid rather than the eye’s surface. Staphylococcus aureus colonizes the eyelid margin and can infect the oil glands (meibomian glands) or hair follicles of the lashes. The bacteria produce toxins that irritate surrounding tissue, causing redness, swelling, and the painful bumps characteristic of styes.
Microscopic mites called Demodex also play a role in chronic eyelid problems. These tiny organisms live at the base of eyelash follicles, feeding on skin cells and causing mechanical damage with their claws. They lay eggs that distort the follicle and produce debris that forms a crusty buildup around the lash base. Demodex is rare in young adults (2 to 27 percent prevalence) but nearly universal after age 70, affecting over 80 percent of people older than 60.
Who Faces Higher Risk
Contact lens wearers face the highest preventable risk, but other groups are also more vulnerable. Young children in group settings pass bacterial conjunctivitis back and forth easily. People who work outdoors or in dusty environments face more corneal abrasions. Anyone with a weakened immune system has a harder time fighting off organisms that healthy eyes can usually handle on their own.
The common thread across nearly all eye infections is that they require a pathogen to physically reach the eye’s surface, whether carried by your fingers, another person’s secretions, contaminated water, or a dirty contact lens. Keeping your hands away from your eyes, caring for lenses properly, and replacing eye cosmetics regularly eliminates most of the ways infections find their way in.