What you must never mix when cleaning: four dangerous pairs

Most household products are safe on their own and dangerous in pairs. The warning is printed in small type, while "I will use everything at once to be sure" is normal domestic logic. Here are four combinations worth knowing.

Bleach and an acidic cleaner

The classic case: the toilet gets a chlorine product, then someone reaches for an acidic limescale remover. The reaction releases chlorine gas — it stings the eyes and catches the breath. In a small windowless bathroom the concentration builds within minutes.

Bleach and ammonia

Ammonia is in many glass cleaners. Mixed with chlorine it produces chloramines, which irritate the airways and, breathed in long enough, cause pulmonary oedema. What makes it worse is that the smell is not always sharp, so people keep working.

Vinegar and baking soda

This one is not dangerous, just pointless: the acid and the alkali neutralise each other, and instead of two working products you get salty water and carbon dioxide. The dramatic fizzing is the sound of nothing happening. Separately, both work very well.

Two different oven cleaners

Alkaline degreasers must not be layered over each other or over acidic products: the reaction happens inside the closed oven, and splashes of hot alkali burn skin. If the first product did not cope, rinse the surface with water before reaching for another.

What this means in practice

• One surface, one product at a time, rinse with water in between
• Open a window and leave the bathroom door open
• Gloves always; a mask as well for aerosols
• Read the "do not mix with…" line on the back of the bottle
• Never decant products into other bottles — the label and the warning go with it

If fumes do build up, leave the room and ventilate rather than finishing the job. Professional teams work with the windows open and never combine products in one room for exactly this reason.