Boric Acid

Boric acid (also known as orthoboric acid or boracic acid) is a weak, monobasic Lewis acid with the chemical formula H₃BO₃ or B(OH)₃. It consists of a central boron atom bonded to three hydroxyl groups. It appears as a colorless or white crystalline solid or powder, is odorless, and dissolves in water. It occurs naturally as the mineral sassolite.

Key Properties

• Molecular weight: 61.83 g/mol
• Appearance: White crystalline solid
• Solubility: Moderately soluble in water (about 49 g/L at 20°C); the aqueous solution is weakly acidic (pH around 5.1 in saturated solution)
• Melting point: Around 171°C, with decomposition above ~100°C releasing water and forming boric anhydride.
• It behaves as a Lewis acid by accepting a hydroxide ion rather than donating a proton directly.

Common Uses

Boric acid has a wide range of applications due to its antifungal, antiseptic, insecticidal, and flame-retardant properties:

• Household and Pest Control: Used in baits, dusts, or powders to control ants, cockroaches, silverfish, termites, and other insects. It acts as a stomach poison or by abrading their exoskeletons. It also helps with algae, molds, fungi, and some weeds.
• Medical and Personal Care:
  • Vaginal suppositories for recurrent yeast infections (especially those caused by non-albicans Candida species like C. glabrata) or to help restore vaginal pH balance and reduce odor. It is typically used as a second-line treatment when standard antifungals fail. These are inserted vaginally (not taken orally).
  • Historically used in dilute solutions as an eyewash or mild antiseptic for minor skin irritations, though modern use is more limited and should follow medical advice.
  • Some ointments or powders for athlete’s foot or other fungal skin issues.
• Industrial:
  • Flame retardant in materials.
  • Precursor for other boron compounds.
  • Neutron absorber in nuclear applications.
  • Wood preservative against decay fungi.
  • Component in some glass, ceramics, and enamels.
• Other: Occasionally in cosmetics (at low concentrations), buffers, or as a mild astringent.

It is available over-the-counter in powder form, suppositories, or as part of pesticide products.

Safety and Hazards

Boric acid is generally considered to have low acute toxicity for most uses when handled properly, but it is not harmless:

• Ingestion: Toxic if swallowed in significant amounts. Symptoms include nausea, vomiting, diarrhea (sometimes blue-green), abdominal pain, skin rash (“boiled lobster” appearance), and in severe cases, kidney damage, seizures, or coma. The minimum lethal dose is roughly 3–6 g for children and 5–20 g for adults. Never ingest boric acid powder or solutions orally.
• Skin and Eyes: Mild irritation possible with prolonged contact; borax (a related compound) can be more irritating or corrosive to eyes. Avoid contact with broken skin or large areas.
• Reproductive Toxicity: Classified as a substance that may damage fertility or the unborn child (Repr. 1B in some regulations). Avoid exposure during pregnancy or if trying to conceive.
• Inhalation: Dust can irritate the respiratory tract.
• Chronic Exposure: Potential effects on kidneys, central nervous system, or reproduction with high/prolonged exposure.

Important Safety Notes:

• Keep away from children and pets.
• Use personal protective equipment (gloves, eye protection) when handling powder.
• For vaginal use, follow medical guidance precisely—do not use if pregnant or with open wounds.
• In case of poisoning, seek immediate medical help or contact poison control. Treatment is supportive (e.g., washing affected areas, fluids).

Boric acid has been used safely for decades in regulated contexts, but always follow product labels and consult a healthcare professional or pharmacist for medical applications