Eye drops are among the most widely used medications globally, helping treat conditions like infections, dry eyes, and childhood myopia. However, a commonly used preservative - Polyhexamethylene biguanide, or PHMB - is now raising concerns among ophthalmologists due to its potential impact on long-term eye health.

PHMB is a powerful antimicrobial agent added to multidose eye drop bottles to prevent bacterial contamination. It works by disrupting microbial cell membranes and genetic material, effectively eliminating harmful organisms such as Pseudomonas and Staphylococcus.

“By disrupting microbial cell membranes and genetic material, it effectively eliminates harmful organisms such as Pseudomonas and Staphylococcus, which can cause serious eye infections. However, while PHMB protects the bottle, emerging scientific evidence suggests it may also affect the delicate tissues of the eye, particularly when used repeatedly over long periods,” said Dr. Mihir Kothari, Pediatric ophthalmologist, Adult squint specialist, Nystagmologist, Adult cataract surgeon.

This makes PHMB highly effective in maintaining the sterility and safety of eye drop formulations, especially those used over multiple days.

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hile PHMB protects the solution inside the bottle, emerging research suggests it may also affect the ocular surface, particularly with long-term use. Laboratory studies indicate that PHMB can:

The concern becomes more significant in children, especially those undergoing long-term treatment for progressive myopia or chronic eye conditions.

Since the paediatric ocular surface is still developing, repeated exposure to preservatives like PHMB may increase inflammation, affect tear film stability, and stress limbal stem cells (essential for corneal repair). Experts warn that this could potentially impact long-term eye health if not carefully managed. “This issue becomes even more significant in children, particularly those receiving long-term treatment for progressive myopia or chronic ocular conditions. Because the paediatric ocular surface is still developing, prolonged exposure to certain preservatives may increase the risk of ocular surface inflammation and potential limbal stem cell stress over time,” said Dr. Kothari.

Because the paediatric ocular surface is still developing, prolonged exposure to certain preservatives may increase the risk of inflammation

Many ophthalmologists are now advising caution, particularly for patients requiring long-term therapy. Key recommendations include:

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