Boric acid is a mild, white powder with a surprisingly wide range of uses, from treating vaginal infections to killing cockroaches to preventing mold. It’s mildly acidic, derived from the mineral boron, and shows up in medical products, pest control formulas, and household cleaners. Here’s what it actually does and how people use it.
Vaginal Infections
The most common medical use for boric acid is as a vaginal suppository to treat yeast infections and bacterial vaginosis (BV), particularly when standard treatments haven’t worked. The suppositories help restore the natural acid balance inside the vagina, creating an environment where yeast and harmful bacteria struggle to thrive.
Boric acid is especially useful against a stubborn type of yeast called Candida glabrata, which has built-in resistance to the most commonly prescribed antifungal medications. In one clinical study of women with diabetes and vaginal yeast infections, boric acid suppositories achieved a 74% cure rate at 15 days, compared to 51% for the standard antifungal. That gap was even wider for Candida glabrata infections specifically.
The typical dose is a 600 mg suppository inserted vaginally once daily. For recurrent BV, the CDC’s treatment guidelines describe a protocol of 600 mg daily for 21 days as part of a multi-step approach following initial antibiotic treatment. These suppositories are meant to be used vaginally only. Swallowing boric acid is dangerous.
Pest Control
Boric acid is one of the oldest and most reliable insecticides for household pests, particularly cockroaches, ants, and silverfish. It works through multiple mechanisms: when insects walk through boric acid powder, the fine crystals scratch and damage their outer shell, causing them to dry out. If they ingest it, either by grooming themselves or eating treated bait, it disrupts their digestive system and damages their nervous system.
This combination makes boric acid effective even in small amounts. It’s commonly sold as a fine powder that you can dust into cracks, behind appliances, and along baseboards where insects travel. It also comes mixed into bait stations and gel formulas. Because it doesn’t break down quickly, a single application can remain effective for months in dry, undisturbed areas.
Mold Prevention and Household Cleaning
Boric acid’s antifungal properties extend beyond the body. Dissolved in water, it works as a mold inhibitor on surfaces like wood, tile grout, and bathroom walls. Some people spray a dilute boric acid solution on areas prone to mildew and let it dry in place as a preventive barrier. It’s also used in laundry as a booster for cleaning and odor control, though borax (a related but chemically distinct compound) is more common for that purpose.
Boric Acid vs. Borax
People often confuse these two, but they’re different chemicals with different strengths. Borax is a naturally occurring mineral that’s alkaline. It’s the one you’ll find in laundry detergent boosters and all-purpose cleaners. Boric acid is made by combining borax with a strong acid, producing a mildly acidic compound. That acidity is what makes boric acid better suited for antiseptic uses, pest control, and mold prevention. Both have an indefinite shelf life, so neither will expire sitting in your cabinet.
Eye and Ear Washes
In very dilute concentrations, boric acid has a long history as a mild antiseptic in eye wash solutions and ear drops. You’ll find it listed as an inactive or buffering ingredient in some over-the-counter eye rinses, where it helps maintain the solution’s pH at a level comfortable for the eye. This use dates back well over a century, though modern products tend to rely on other preservatives and buffering agents as primary ingredients.
Toxicity and Safety Risks
Boric acid is safe in the specific ways it’s meant to be used, but it’s genuinely toxic if swallowed. Symptoms of boric acid poisoning include blue-green vomit, diarrhea, a bright red skin rash, seizures, and in severe cases, coma or collapse. Even smaller ingested amounts can cause headache, drowsiness, and fever. This is why vaginal suppositories should never be taken orally, and why powder used for pest control needs to be placed where children can’t reach it.
Pets are also at risk. Dogs and cats that ingest boric acid, whether by licking treated surfaces or getting into powder containers, can develop vomiting, diarrhea, muscle tremors, and seizures. Borates absorb rapidly through the gut and through damaged skin. Chronic low-level exposure in pets can cause dry skin and hair loss. If you’re using boric acid for pest control in a home with animals, placement matters: keep it inside wall voids, behind heavy appliances, and in areas your pets genuinely cannot access.
Skin contact with boric acid powder is generally not harmful in brief, incidental exposure, but prolonged contact or application to broken skin can cause irritation and allow absorption into the body. Standard practice is to wash it off promptly if it contacts your skin or eyes directly.