Trachoma is a bacterial eye infection that, left untreated over years, scars the inner eyelid and eventually causes blindness. It is the leading infectious cause of blindness worldwide, driven by repeated infections with a bacterium called Chlamydia trachomatis. The disease primarily affects communities living in poverty, where overcrowding, limited water access, and poor sanitation allow the infection to cycle through households, particularly among young children.
What Causes Trachoma
The bacterium behind trachoma, Chlamydia trachomatis, comes in several varieties. The strains responsible for trachoma (known as serovars A, B, Ba, and C) specifically target the surface of the eye. These are genetically distinct from the strains that cause genital chlamydia infections. One key difference is a mutation in a gene involved in producing the amino acid tryptophan, which helps researchers tell ocular and genital strains apart.
The infection spreads through direct contact with eye or nose discharge from an infected person, typically via hands, shared towels, bedding, or clothing. Certain species of flies also play a major role: they land on the face of an infected child, pick up discharge, then carry it to the next person. Young children are the primary reservoir of infection, and in endemic communities, kids may be reinfected dozens of times throughout childhood.
How Trachoma Leads to Blindness
Trachoma doesn’t blind people with a single infection. It’s a slow, cumulative process that unfolds over decades. In childhood, each bout of infection triggers inflammation on the inner surface of the upper eyelid (the conjunctiva). Most of these episodes are mild, even subclinical, meaning a child may not notice anything beyond some eye discharge or mild irritation. But each round of infection provokes an immune response that, over time, deposits scar tissue on the inner eyelid.
Mathematical models based on field observations estimate that more than 100 conjunctival infections over a person’s lifetime are needed to produce significant scarring, and roughly 150 infections to reach the stage where eyelashes begin turning inward. That scarring gradually distorts the eyelid, a condition called entropion, causing the eyelashes to scrape against the cornea with every blink. This is called trichiasis. The constant abrasion of lashes on the cornea creates ulcers and clouding (corneal opacity), which progressively destroys vision.
The underlying biology involves infected cells on the eye’s surface releasing inflammatory signals that recruit immune cells to the area. Over many rounds of infection, this chronic inflammation reshapes the tissue, replacing normal conjunctival lining with dense scar tissue. By the time trichiasis develops, usually in adulthood, the disease is no longer infectious. It has become a mechanical problem: scarred tissue pulling lashes into the eye.
The Five Clinical Stages
The WHO uses a simplified grading system that identifies five signs of trachoma, roughly corresponding to how the disease progresses:
- Trachomatous inflammation, follicular: Small raised bumps (follicles) appear on the inner surface of the upper eyelid. At least five follicles, each about half a millimeter across, must be visible for this diagnosis. This is the earliest sign and is most common in children.
- Trachomatous inflammation, intense: The inner eyelid becomes so swollen and inflamed that the normal blood vessels beneath it are no longer visible. This stage signals heavy, ongoing infection.
- Trachomatous scarring: White lines or bands of scar tissue become visible on the inner upper eyelid. At this point, structural damage is accumulating.
- Trachomatous trichiasis: At least one eyelash from the upper lid turns inward and touches the eyeball. Some people pull out the offending lashes themselves (epilation), but they grow back.
- Corneal opacity: The cornea becomes clouded enough that the edge of the pupil is blurred when viewed through the haze. This is the stage at which vision loss becomes significant or irreversible.
The first two stages are considered “active trachoma” and respond to antibiotics. The last three are consequences of past damage and require different management.
Who Is Most at Risk
Trachoma clusters in communities with limited access to clean water, inadequate sanitation, and crowded living conditions. When families share sleeping spaces and have little water available for face-washing, the bacterium passes easily between household members. Children under 10 are most frequently infected and reinfected, and women are disproportionately affected by the blinding complications later in life, likely because they spend more time in close contact with young children.
Flies thrive near open latrines and animal waste, and in communities without proper sanitation, fly populations are high enough to serve as a significant transmission route. The link between trachoma and poverty is so strong that improvements in living standards alone have historically eliminated the disease from parts of the world where it was once common, including much of Europe and North America.
The SAFE Strategy
The WHO’s approach to eliminating trachoma is built around four interventions, known by the acronym SAFE:
- Surgery for people who already have trichiasis. The recommended procedure (bilamellar tarsal rotation) involves cutting through the scarred eyelid tissue and rotating the lid margin outward so the lashes no longer scrape the cornea. An estimated 2.8 million people currently need this surgery. It can be performed by trained non-physician health workers in community settings, which is critical in remote areas.
- Antibiotics to clear active infection. Mass drug administration programs distribute oral azithromycin (a single dose, typically once or twice a year) to entire communities where active trachoma is prevalent. The goal is not just to treat individuals but to reduce the overall amount of bacteria circulating in a community. In areas where trachoma prevention programs are already running, children may need only one additional dose per year.
- Facial cleanliness through hygiene education, especially teaching children and caregivers to wash faces regularly. Clean faces with no visible eye or nose discharge are far less attractive to the flies that spread infection.
- Environmental improvement, including better access to water and sanitation. Building latrines reduces fly breeding sites. Increasing water availability makes regular face-washing practical rather than theoretical.
All four components work together. Surgery prevents blindness in people already affected. Antibiotics reduce transmission. Facial cleanliness and sanitation prevent reinfection. Without the environmental pieces, antibiotic treatment alone tends to produce temporary results, with infection bouncing back once treatment stops.
Progress Toward Elimination
The WHO has set specific thresholds for declaring trachoma eliminated as a public health problem in a given country. A district must show less than 5% of children aged 1 to 9 with active inflammatory trachoma, and fewer than 0.2% of adults aged 15 and older with untreated trichiasis. The country must also have a functioning system to detect and manage new trichiasis cases as they arise.
Multiple countries have achieved validated elimination in recent years, and the WHO tracks progress through a global database updated annually. The most recent snapshot, from April 2025, shows continued gains, though trachoma remains endemic in parts of Africa, the Middle East, Central and Southeast Asia, and some Pacific Island nations. The overall trajectory is encouraging: the number of people requiring surgery and antibiotics has dropped substantially over the past two decades, driven largely by the scale-up of the SAFE strategy.
What Living With Trachoma Looks Like
For a child in an endemic community, trachoma often feels like a recurring eye irritation: red, watery eyes, discharge that crusts around the lids, mild sensitivity to light. Many children experience it so frequently that it seems normal. These episodes typically resolve on their own or with treatment, and most children do not develop long-term complications if transmission is interrupted early enough.
For an adult who has progressed to trichiasis, the experience is far more painful. Eyelashes scraping the cornea with every blink causes constant pain, light sensitivity, and tearing. Many people resort to pulling out the offending lashes with tweezers, but this is temporary relief since the lashes grow back within weeks. Without surgery, the repeated corneal damage gradually clouds vision, often to the point of functional blindness. The impact goes beyond the eyes: blindness in these settings typically means loss of livelihood, dependence on family members, and social isolation.