Why You Should Never Mix Cleaning Products

The short rule

Use one cleaning product at a time, and do not combine products unless the label explicitly says it is safe. Many cleaners are made to work on their own, and their ingredients can react with each other in ways that are not obvious from the labels. The result can be a gas that irritates or damages the eyes, nose, throat and lungs.

Accidents of this kind usually happen when someone is trying to do a better job: adding a second product to boost a stubborn stain, or using a different cleaner straight after the first. The intention is reasonable. The outcome can be serious.

Why mixing can go wrong

A cleaner is a chemical mixture designed for a certain job. When two such mixtures meet, their ingredients can react. Some reactions make heat, some make gas, and some produce new substances more harmful than either product alone. Because most people do not know the full ingredient list or the chemistry, it is difficult to predict which combinations are safe. The simplest and safest approach is not to experiment.

Combinations that are well known to be hazardous

These are examples, not a complete list.

• Bleach and ammonia. Household bleach (sodium hypochlorite) can react with ammonia, which is found in some glass and multi-surface cleaners, to produce toxic chloramine vapours. These can cause coughing, shortness of breath, chest pain and irritation of the eyes and throat. Ammonia is also present in urine, so cleaning a soiled area with bleach after an accident is something to avoid as well.
• Bleach and acids. Bleach mixed with acidic products, including many toilet bowl cleaners, limescale removers, rust removers and even vinegar, can release chlorine gas. Chlorine is a respiratory irritant, and even short exposure in a small room can be dangerous.
• Bleach and rubbing alcohol (and some other alcohol-based products). The combination can form harmful compounds, including chloroform in certain conditions.
• Hydrogen peroxide and vinegar in the same container can form peracetic acid, which is corrosive and can irritate skin, eyes and lungs.
• Different drain cleaners. Using one product, then another when the first fails, can cause a violent reaction, heat and splashing in the drain, as well as fumes.

The pantry staples covered in the explanation of cleaning chemistry basics are not exempt. Vinegar with bleach is hazardous, and a vinegar and bicarbonate mixture fizzes but largely neutralises itself, and should never be sealed in a bottle.

Hidden ways products end up mixed

You do not have to pour two bottles together to create a mix.

• Using products in sequence on the same surface. Spraying a toilet with an acid-based cleaner and then adding bleach before the first is rinsed away creates the same hazard.
• Residue in the bottle. Topping up a spray bottle that held a different product, or re-using a container without rinsing it thoroughly, mixes old and new.
• Drains and toilets. Products poured down the same drain can meet in the pipe, which is another reason leftovers should not be poured away, as covered in the guide to chemical disposal.
• Cloths and sponges. A cloth soaked in one product and then used with another can carry it over.
• Storing products on top of each other. A leak from one onto another can create a mix, a point also made in the advice on chemical storage.

What the labels may say

Many labels carry precautionary lines such as “do not use with other products” or “never mix with bleach or acids”. These warnings are worth looking for, and the symbols and statements on a pack are explained in the guide to hazard symbols. If the label says nothing, that does not mean mixing is safe.

What to do if you mix products by accident

These are general first steps. Follow any instruction on the product labels, and local emergency advice takes priority.

1. Stop and get away from the fumes. If you smell something sharp or chemical, or begin to cough or feel your eyes sting, leave the room immediately.
2. Get fresh air. Go outdoors if you can. Take children, other adults and pets with you. Open windows and doors only if you can do so without staying in the affected space.
3. Do not try to clean up while the fumes are strong. Do not add water or another product on the assumption that it will dilute the problem.
4. Seek help if anyone has symptoms. Coughing, wheezing, chest tightness, difficulty breathing, burning eyes, nausea or a headache after exposure all justify calling your local poison helpline or emergency services. Call emergency services straight away for severe breathing difficulty, collapse or chest pain.
5. If skin or eyes were splashed, follow the first-aid directions on the label, which typically include rinsing with plenty of running water for several minutes. Remove contaminated clothing.
6. Return only when the air is clear. Ventilate the area well and allow time for the fumes to disperse before going back. If you are unsure, ask a professional such as the fire service or poison helpline.
7. Keep the packaging so you can tell responders exactly which products were involved.

People with asthma, heart or lung conditions, as well as young children and older people, are generally more vulnerable, so take any exposure seriously even if you feel only mildly affected, and ask for advice.

Safer habits

• Use one product at a time and rinse the surface with water before using another, if you must change products.
• Keep products in their original, labelled containers.
• Never decant into unmarked bottles or reuse containers without thorough rinsing.
• Ventilate the room by opening windows when cleaning, and avoid small closed spaces such as a shower cubicle with the door shut.
• Be cautious with homemade recipes found online that combine ingredients, and note that homemade cleaners are not tested or preserved like commercial products. If a recipe says to combine bleach, ammonia or strong acids, do not follow it.
• If a cleaner is not working, step back. Consider a different approach, such as soaking, scrubbing, waiting, or calling a professional for drains and stubborn problems, rather than adding another product.
• Choosing products with simple, well-labelled formulas can help, and our look at eco-friendly cleaners discusses what to check.

This is general information, not medical or professional advice. In an emergency, contact your local emergency services or poison helpline.