Ask the Doctors: Saliva a key defense against toxins, microorganisms

Dear Doctors: Our 9-year-old loves science and has become obsessed with saliva. He recently learned in school that it helps prevent disease, and now he wants to know more. What is saliva? Does it really help people stay healthy?

Dear Reader: Saliva is a crucial line of defense. It makes sense, considering the mouth is a key entryway for potential pathogens like dangerous microorganisms or toxins that might be in food or drink, as well as those that can hitch a ride into the mouth on fingers, surfaces, objects or even a kiss.

While awake, a healthy person produces 2 or more pints of saliva a day. During sleep, that drops to near zero. The majority comes from three major pairs of salivary glands, with additional amounts coming from hundreds of minor glands. The fluid these glands produce lubricates the mouth and throat, moistens food so that it can be chewed and swallowed, makes possible the sense of taste and washes away particulates. Because saliva has a near-neutral pH of 6.3, it helps protect tooth enamel by maintaining the acid-base balance in the mouth. And while it’s made up of 99% water, the remaining 1% contains important organic and inorganic molecules. That makes saliva a biofluid.

Some of the compounds in saliva, including the enzymes lipase and amylase, kick-start digestion by beginning to dismantle fats and carbohydrates as you chew. Others play an important role in protecting the body from disease. Saliva is stocked with antiviral, antimicrobial and antifungal compounds. These include hydrogen peroxide, lactoferrin and simple proteins that dismantle, damage and neutralize many potential pathogens.

Research has found that tiny sugar molecules in saliva, known as glycans, play an important role in preventing a certain fungus that is present in the mouth from becoming a health problem. Saliva also contains compounds that play an important role in wound healing. When you accidentally bite your tongue or chew your cheek, the injury heals surprisingly fast. Saliva is the reason.

Also, some people might have undergone a so-called “spit test” for COVID-19, which identifies the SARS-CoV-2 virus more quickly and comfortably than with nasal swabs. Researchers are also learning that various proteins and other compounds in saliva become detectably altered in response to certain types of disease. These discoveries have led to a promising new screening test for oral pre-cancers and cancers.

Dr. Eve Glazier and Dr. Elizabeth Ko are internists at UCLA Health.