Preservatives often get a bad rap, but they’re necessary in keeping foods and products fresh. You might also come across them in eye drops used to treat dry eyes.
BAK (benzalkonium chloride), one of the most popular ophthalmic preservatives, has been linked with ocular surface toxicity. Patients taking multiple BAK-preserved medicines or who already suffer from preexisting ocular surface disease could potentially benefit from switching to preservative-free regimens in order to limit cumulative BAK exposure and thus limit cumulative damage.
Preservatives in Food
Preservatives used to preserve foods include antimicrobials and antioxidants. These ingredients work to prevent spoilage by inhibiting microbial growth or slowing chemical reactions; they’re found in processed and packaged food such as potato chips, instant tea and cake mixes; they may even be added to homemade pickles and jams to extend shelf life.
Some individuals may worry about preservatives in food, but in general they are safe. Preservatives undergo extensive testing and regulation before being approved for use at food-grade levels.
Most chemicals added to food are colorless or clear liquids that do not alter its appearance, while some additives can trigger allergic reactions in some people, including sulphite preservatives that could trigger asthma symptoms of shortness of breath and wheezing in sensitive individuals.
Preservatives in Cosmetics
Preservatives are essential components in the fight against contamination in cosmetic products like lotions, cleansers, toothpaste and shampoo. Preservatives protect these items against infections or spoilage caused by fungus, bacteria or yeast growth that could compromise them over time.
Preservatives in cosmetic formulations come with their own set of advantages and drawbacks, so selecting the ideal preservative depends on various criteria including product ingredients, storage conditions and shelf life requirements.
As cosmetic products must contain preservatives to remain shelf stable for extended use, many popular ingredients used as preservatives include parabens, formaldehyde releasers, isothiazolinones and phenoxyethanol are highly popular choices; other popular preservatives are sorbic acid, capsaicin and organic acids as well.
Many of these ingredients are multifunctional, serving both as preservatives and surfactants or humectants. Chelating agents such as EDTA and GLDA also contain antimicrobial properties by binding to metal ions essential for microbial growth, providing better preservation with lower preservative levels and greater coverage against potential issues. When formulations are designed with multiple preservatives in mind, better preservation can be accomplished while keeping antimicrobial coverage widening over time.
Preservatives in Eye Drops
Preservatives are essential in keeping eye drops sterile, yet prolonged contact can have adverse effects on ocular surfaces – manifested as lachrymal film dysfunction, dotted keratitis or toxic keratopathy (see the image below).
There are various alternatives to benzalkonium chloride available in multidose bottle formulations. Such options as Polyquad (r) and Purite(r), for instance, are stabilized oxychloro complexes which break down into sodium chloride ions, oxygen, and water upon exposure to light.
Other lubricating drops contain gentle preservatives like perfluorocarbons and naphthalene that are much gentler on the eye, such as perfluorocarbons. Studies conducted using cell cultures and clinical research indicate these formulations cause less ocular surface disruption compared with BAK-preserved solutions; switch studies have also demonstrated this fact; they show signs and symptoms of dry eye are significantly improved after patients switch from BAK-preserved drops (see decision tree below)1
Preservatives in Contact Lenses
Most multipurpose contact lens solutions contain preservatives as a safeguard against contamination by micro-organisms such as bacteria, which can cause problems from mild eye redness to potentially vision-threatening eye infections.
Benzalkonium chloride (BAK) is the primary preservative in modern contact lens solutions, but has long been subject to debate and misinformation about its safety. Still, BAK remains an effective antimicrobial agent.
Chlorhexidine gluconate was one of the earliest biocides used in contact lens care systems, acting primarily against bacteria by disrupting their cell membrane. Because it does not bind readily with lenses and thus remain on ocular surfaces without transference, its effectiveness remains intact.
Hydrogen peroxide solutions are generally preservative-free and may be better suited for people who have allergies to disinfecting agents found in multipurpose contact lens solutions. However, it must be neutralized after each use to avoid stinging or injury to the eyes.
