Is your eye drop safe? Experts warn against using brands that contain toxic Polyhexamethylene Biguanide - 'It can damage the ocular surface'

Beware! PHMB in your eye drops could be secretly harming your ocular surface. PHMB is a powerful antimicrobial preservative added to eye drops to prevent bacterial contamination in multidose bottles.

Eye drops are among the most commonly used medications worldwide, treating conditions ranging from infections to dry eyes and childhood myopia. Yet an ingredient quietly present in many multidose eye drop bottles may be raising concern among eye specialists: Polyhexamethylene biguanide (PHMB). In this article, let's understand why it's important to understand the ingredients in eye drops and why PHMB in it can be the worst thing.

What Is Polyhexamethylene Biguanide (PHMB)?

In an exclusive interaction with TheHealthSite.com, Dr Mihir Kothari, Pediatric ophthalmologist, Adult squint specialist, Nystagmologist, Adult cataract surgeon, explains thatPHMB is a powerful antimicrobial preservative added to eye drops to prevent bacterial contamination in multidose bottles. 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.

How PHMB May Affect the Eye?

Laboratory studies have shown that PHMB can trigger cellular stress and apoptosis in human corneal and conjunctival epithelial cells at concentrations similar to those used in ophthalmic preparations. Clinically, chronic exposure to such preserved eye drops has been associated with

1. Ocular surface irritation
2. Tear film instability
3. Corneal staining
4. Dryness, and
5. Delayed epithelial healing

For patients requiring short-term treatment, these effects may be minimal. But concerns grow when eye drops are used daily for months or years.

Why Is the Risk Greater in Children?

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.

Many ophthalmologists are therefore calling for greater caution in the use of PHMB in eye drops intended for long-term therapy in children. In situations where patients require prolonged treatment, especially paediatric patients, preservative exposure should be minimized wherever possible.

Fortunately, ophthalmic technology has advanced significantly. Ionic buffer based preservative-free systems are now available that maintain sterility of multidose eye drops while eliminating the need to add harmful preservatives. These newer systems help protect the ocular surface while ensuring the microbiological safety of the formulation.

With increasing global attention on childhood myopia and long-term ocular therapies, experts believe it may be time for eye drop manufacturers to re-evaluate the routine use of potentially cytotoxic preservatives in chronic ophthalmic medications.

After all, protecting vision is not only about treating disease, but also about preserving the delicate surface of the eye itself