Borax, also known as sodium borate, is a naturally occurring mineral composed of sodium, boron, oxygen and water. It has a wide range of household and industrial applications, including as a cleaning agent, flux for soldering, an anti-fungal treatment, insecticide, herbicide, and fire retardant.
While borax is generally considered safe when used properly, there are some substances that should not be mixed with it. Combining borax with certain other chemicals can produce dangerous reactions, release toxic fumes, or diminish the effectiveness of the borax. Being aware of these incompatibilities helps ensure borax is used safely and appropriately.
Acids
One of the major categories of substances that should never be mixed with borax are acids. When borax interacts with an acid, dangerous reactions can occur.
Acids that should be avoided include:
- Hydrochloric acid – Mixing borax with hydrochloric acid produces chlorine gas, which is highly toxic if inhaled.
- Sulfuric acid – Borax reacts vigorously with sulfuric acid, creating a risk of splashing and release of heat. The reaction also produces boron sulfate, which is irritating and toxic.
- Nitric acid – Contact between borax and nitric acid can create toxic nitric oxide fumes.
- Acetic acid – Borax reacts exothermically with acetic acid, meaning the mixture heats rapidly as a result of the chemical reaction. This poses a risk of boiling, splashing, and release of toxic vapors.
- Oxalic acid – An explosive reaction occurs when borax is mixed with oxalic acid.
- Phosphoric acid – Heating occurs when borax comes into contact with phosphoric acid, bringing risks of spattering, splashing, and emission of toxic fumes.
The general rule is borax should never be mixed with any corrosive acid, as dangerous chemical reactions are likely to occur. Even weak acids like citric acid and ascorbic acid should not be combined with borax.
Bleach
Mixing borax with bleach (sodium hypochlorite) or other chlorine-based bleaches produces toxic chlorine gas. Exposure to chlorine gas can cause burning of the eyes, throat, and nose, coughing, chest tightness, nausea, and fluid buildup in the lungs (pulmonary edema).
Never mix borax with bleach or use borax to clean something that has been cleaned with bleach. Always make sure surfaces are thoroughly rinsed of any bleach residue before applying borax.
Ammonia
Like bleach, ammonia reacts with borax to generate toxic vapors. Specifically, mixing borax and ammonia releases ammonium borate, which decomposes to boric acid and ammonia gas.
Inhaling ammonia gas can damage the airways and lungs. Exposure causes a burning sensation in the throat and nose, cough, chest tightness, difficulty breathing, and fluid in the lungs. Higher exposures can be fatal.
Never clean with borax in areas where ammonia is present. Rinse surfaces thoroughly after using ammonia-based cleaners before borax application.
Vinegar
Though not as dangerous as some other substances, vinegar (acetic acid) should still always be kept away from borax. Mixing vinegar and borax produces a chemical reaction that reduces the effectiveness of the borax.
The acidic vinegar reacts with the basic borax, neutralizing the pH. This makes the borax less alkaline, which diminishes its abilities as a cleaner, laundry booster, and insecticide.
Only use vinegar and borax at different times and make sure to rinse surfaces between application. Never mix the two together.
Citrus
Citric acid and ascorbic acid are weak acids found in citrus fruits like lemons, limes, oranges, and grapefruit. Though not as hazardous as some stronger acids, citric acid can still react with borax in ways that are detrimental.
When borax and citrus juice come into contact, the citric acid neutralizes the alkaline borax. This reduces the cleaning, deodorizing, and disinfecting power of the borax.
Always clean up any citrus spills or residues before applying borax to a surface. Never mix borax directly with citrus juice.
Aluminum
Mixing borax with aluminum produces hydrogen gas, which is highly flammable. This creates a fire and explosion hazard.
The reaction can occur if borax is used on aluminum surfaces. It is also a risk if borax is added to water boiled in an aluminum pot. The heat accelerates the chemical reaction.
Borax should never be used to clean aluminum, cookware, or utensils. Avoid using it in washing machines, dishwashers, or other appliances containing aluminum parts.
Steel
While not as reactive as aluminum, mixing borax with steel should still be avoided. Borax can corrode and pit the surface of steel.
The borax accelerates oxidation of the steel, forming iron oxide (rust) more rapidly than under normal conditions. This damages the steel over time.
Borax should not be used to clean stainless steel sinks, appliances, cookware, utensils, or other steel surfaces. Always rinse borax off of stainless steel as soon as possible after application.
Copper
As with aluminum and steel, borax can react with copper to cause corrosion. The combination of borax and copper produces copper oxides and copper borate complexes.
This interaction means borax should never be used to clean copper surfaces. Avoid using it on copper pipes or in dishwashers and washing machines containing copper parts.
Silver
Borax causes silver to tarnish as sulfur compounds in the borax react with the surface of the silver. This creates a darkened, stained appearance on silver jewelry, tableware, and other items.
To prevent tarnishing, borax should not come into contact with silverware. Do not hand wash silver items with borax and avoid borax in dishwashers used to clean silver.
Concrete
While borax does not directly react with concrete, it can degrade concrete surfaces over time. Borax is alkaline, while concrete is acidic. This mismatch in pH damages concrete when the two are in frequent contact.
Use caution when applying borax as a cleaner to concrete countertops, floors, or other surfaces. Opt for milder, pH-neutral cleaners whenever possible.
Latex
The alkaline borax can break down latex materials like rubber gloves, condoms, latex paint, and adhesives. The borax causes the latex to degrade and lose its elasticity.
Avoid exposing latex materials to borax. Use nitrile gloves when handling concentrated borax solutions. Do not paint latex paint over borax coatings.
Fiberglass
The glass fibers in fiberglass begin dissolving when exposed to borax, eventually causing structural failure. This is a result of the alkaline borax disrupting the epoxy binder in fiberglass products.
Never use borax on fiberglass tubs, sinks, boat hulls, auto bodies, or other fiberglass materials. The damage may not be immediately visible but can lead to product failure over time.
Plant life
Borax is phytotoxic, meaning it is directly toxic to plants. The boron in borax accumulates and interferes with the metabolism of plants when absorbed through the roots and leaves. This causes yellowing, stunted growth, and eventual plant death.
Never apply borax directly to or around garden plants, landscaping, potted plants, food crops, or areas where vegetation growth is desired. Borax should only be used for controlling weeds in cracks in pavement, gravel lots, or other locations where plant life is unwanted.
Pets
Borax can be harmful if ingested by pets, especially dogs. The boron in borax can accumulate to toxic levels in an animal’s body with repeated exposure. Early signs of borax poisoning in pets include vomiting, diarrhea, tremors and seizures.
Keep borax inaccessible to pets by storing it in high, locked cabinets. Never apply borax directly to pet bedding, crates, kennels or living areas. Use with caution even on carpets and floors that pets have access to.
Fish and reptiles
Aquatic life including fish, reptiles, and amphibians are highly sensitive to boron. Borax that washes into ponds, lakes, and oceans or leaches into groundwater can be lethal even in low concentrations.
Never use borax near bodies of water, wetlands, or shorelines where runoff contamination is a risk. Use extreme caution when applying outdoors or to exterior surfaces where rain can carry borax into storm drains or groundwater.
Septic systems
The alkalinity of borax can harm the bacteria responsible for breaking down waste in septic systems. When added to septic tanks, it can reduce efficiency and lead to system failure.
Borax should never be poured directly into a septic tank or drain field. Use sparingly in laundry, cleaning, and other applications on properties using septic systems.
Look for septic safe alternatives when possible to reduce total borax loading. Only use the minimal amount needed for cleaning effectiveness.
Products containing sodium metaborate
Sodium metaborate (NaBO2) reacts explosively with borax. The reaction between the two chemicals is dangerously exothermic, rapidly generating intense heat.
Always check product labels and avoid combining borax with drain cleaners, commercial oven cleaners, or rust removal solutions containing sodium metaborate. Carefully rinse any sodium metaborate residue from surfaces before applying borax.
Other boron compounds
Combining different boron compounds can be hazardous as the concentration of boron greatly increases. Possible reactions include violent boiling, splattering, and release of toxic fumes.
Never mix borax with boric acid, sodium perborate, or other boron-containing chemicals. Only use one boron compound at a time and thoroughly rinse surfaces between uses of different boron cleaners.
Products containing zinc
When borax and zinc compounds combine, flammable and explosive hydrogen gas can be generated. This gas may be immediately ignited by friction, heat, or static charge.
Avoid mixing borax with zinc-based anti-rust treatments, automotive body fillers, paints containing zinc oxide, and other zinc-containing materials. Rinse surfaces to remove zinc residues before applying borax.
Photographic chemicals
Borax should not be used to clean around darkrooms or photographic studios. When it mixes with developers, stop baths, and photographic fixing agents, the borax can create insoluble borates that leave residue on surfaces.
The borax residue damages films and prints during the development process. Use borax-free cleaners and detergents designed for photographic studios and darkrooms.
Water-reactive substances
Borax can react vigorously when mixed with water-reactive chemicals like calcium carbide, calcium hypochlorite, aluminum bromide, and magnesium sulfate. Violent reactions with spattering or boiling can occur.
Never add borax to any chemical that hisses, bubbles, smokes, or becomes hot when mixed with water. Carefully rinse any water-reactive residue from surfaces before using borax.
Peroxides
Combining borax with peroxides like hydrogen peroxide (H2O2) generates additional oxygen gas through decomposition of the peroxide.
If done in an enclosed container, pressure buildup from the released oxygen can cause an explosion hazard. Use borax and peroxides separately with thorough rinsing between applications.
Strong oxidizers
Chemicals like chlorine, bromine, and fluorine are strong oxidizing agents and can react vigorously when mixed with borax. Potential hazards include intense heat, boiling, splattering, and release of toxic fumes.
Never mix borax with pool chemicals, oxidizing bleaches, chlorine sanitizers, and similar corrosive oxidizers. Rinse surfaces to remove all traces before using borax.
Borax Safety and Usage Tips
While borax has many useful applications, it also carries risks if used improperly or combined with incompatible materials. Follow these tips for safe use of borax:
- Read product labels and follow instructions carefully.
- Never mix borax with other cleaners or chemicals unless specifically stated as safe to do so.
- Store borax securely out of reach of children and pets.
- Wear gloves and avoid inhaling borax dust.
- Use diluted solutions and only use the amount needed for the task.
- Rinse surfaces thoroughly after using borax, especially before reapplying another cleaner.
- Avoid use on aluminum, steel, silver, latex, fiberglass and other incompatible materials.
- Never dispose of borax in drains connected to septic systems.
- Carefully rinse borax off produce and surfaces used for food preparation.
Being aware of what not to mix with borax allows you to utilize its benefits while minimizing risks. Take care when using borax around pregnant women, babies, pets, plants, and people with sensitivities. With safe handling, borax can be an effective component of your cleaning routine.
Conclusion
Borax is a versatile cleaning and disinfecting product, but should be used with caution. Mixing borax with acidic or oxidizing chemicals can result in dangerous reactions producing toxic fumes and heat. It can also damage surfaces when used on inappropriate materials. Key things to avoid mixing borax with include bleach, ammonia, acids, vinegar, aluminum, copper, latex, fiberglass, photographic chemicals and septic systems. Taking proper precautions allows you to safely take advantage of the stain-fighting, anti-fungal, and odor-eliminating properties of borax. Be sure to read labels, follow usage guidelines and rinse surfaces completely between applications. Knowing what not to combine with borax is crucial for using this cleaning staple effectively while protecting yourself, others, pets and property.