After numerous news reports about infections, such as H1N1 and the avian flu, I was astounded when a patient removed her contact lens and popped it in her mouth. She could tell by my expression that I was not pleased, yet she coolly said to me, ”What? I do this all the time and have never had a problem!”

If our patients partake in this practice regularly, why don’t we see more complications? And, what is so bad about this little ritual, after all?

How Clean is the Mouth?
The mouth is a busy place. It provides an excellent supportive environment for almost 600 varieties of organisms, including many types of bacteria, fungi, mycoplasms, protozoa and viruses.1,2 In fact, saliva contains an estimated 109 bacteria per milliliter.3 This represents one of the most concentrated microbial populations anywhere in the body.4 Realistically, however, it is difficult to estimate an individual’s oral bio-load. Variations in dental anatomy, salivary components, pH and diet regulate the flora present at any given moment.5,6

In some cultures, saliva is considered a natural disinfectant, and animals are encouraged to lick wounds to promote healing. Studies have shown that wound licking does speed healing in certain species and with certain injuries, but there are no studies to show the benefit of the human mouth, and the risks certainly outweigh the benefits.7,8

Ninety-eight percent of saliva is water, while the other 2% consists of electrolytes, mucus, antibacterial compounds and various enzymes.9 These components—which include products that are antibacterial, antiviral and antifungal, as well as tissue-coating, lubricating, mineralizing, digesting and buffering—all act to regulate oral flora and protect against pathogens. Most of these components are benign to the ocular surface, and in some severe dry eye patients, salivary glands are transplanted to lubricate the ocular surface. While you may not like the sound of patients placing digesting or mineralizing agents on their contact lenses, their interaction is generally brief and probably have no lasting effect on the eye. The microbiology involved, however, is a different story. The most prevalent bacteria in saliva are Staphylococcus spp. (85.7%), Pseudomonas spp. (83.8%) and Acinetobacter spp. (53.3%).10

The Eye’s Natural Defenses
The greatest protection against these pathogens is not the oral antimicrobial activity but the normal barrier defenses of the eye. Intact epithelial layers, plentiful tear components and blinking help flush the eye out and prevent ocular surface infection.11,12 Immunoglobulins and lysozymes are important and powerful tear film defenses against many infectious diseases. Lysozyme concentration in tears is higher than in any other bodily fluid. Lysozyme levels decrease with age, in cases of both Sjögren’s syndrome and blepharitis and in smokers, but generally provides a good defense.13-18

Fight the Urge to Lick
So what are the chances of getting an ocular infection after giving your lens a licking? Probably fairly low, if you have an intact defense mechanism. But, do we always know when our barriers are intact or what pathogens are lurking between our teeth? It’s unlikely. Just ask my patient who used saliva to insert her contact lens when it dislodged during a corneal paper cut incident. She’ll tell you about her third corneal transplant. 

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18. Sariri R, Ghafoori H. Tear proteins in health, disease, and contact lens wear. Biochemistry (Mosc). 2008 Apr;73(4):381-92.