Read the bottle before cleaning the room.

The bathroom is small, the door is closed and the cleaner says to use it in a well-ventilated area. Solve that part before opening the bottle. More product and a stronger smell do not establish that a surface is cleaner.

Read the use, dilution, ventilation and protective-equipment directions on the original container. Check that the product is intended for the surface and task. A spray for one material may be unsuitable for another.

Use the stated amount and application method. Do not turn a liquid product into a spray or add an ingredient to improve it. If the label requires a contact time, plan for that without leaving the product accessible to children or pets.

Arrange the specified ventilation during and after use. An outside-venting exhaust fan and suitable window opening may help, depending on the room and instructions. A recirculating fan moves air around; it does not by itself remove vapours outdoors.

If weather or outdoor smoke prevents adequate ventilation for an optional task, postpone it or choose an appropriate alternative method. Do not rely on a particle purifier to make a poorly ventilated chemical task suitable.

Health Canada advises never mixing household chemical products. Transport Canada explains that bleach mixed with acids or ammonia can release dangerous gases. This includes improvised combinations using products that seem familiar, such as vinegar.

Avoid layering different cleaners on the same surface without following their directions. Keep the original labels, and never decant a cleaner into a food or drink container.

Close caps promptly, wash your hands after use and put products away as directed. Buy quantities you can use rather than building an unexplained collection under the sink.

Keep a simple record when a particular product repeatedly causes an unpleasant reaction: its exact name, how it was used and the room conditions. That gives the manufacturer or a health professional something more useful than 'the bathroom smelled strong'.

If an accidental mixture releases fumes, leave the area for fresh air. Do not lean over it, add another chemical or stay to finish the cleaning. Get immediate poison-centre or medical advice; call emergency services for severe breathing difficulty or another emergency.

Good ventilation belongs in the preparation, alongside the cloth and gloves. It is much easier to arrange before the room is full of cleaning supplies.