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Why you shouldn’t mix these household cleaning products to avoid harming yourself

Be careful with that bleach! Like a chemistry experiment gone wrong, you could end up hurting yourself while doing chores such as cleaning the bathroom or the oven.

These days, with the pandemic and all, you may be more particular about your home’s cleanliness, and may be cleaning and disinfecting more often than usual. 

So, you bring out the big guns such as bleach-based household cleaners. Those who prefer more “natural” cleaning solutions may be resorting to using vinegar, baking soda, lemon juice – or whatever the latest YouTube video recommends.

But your best intentions to get your home safe for yourself and your family could potentially go awry. Like a Mentos and Coke experiment, certain chemicals are just not meant to be mixed – as the result could be a lot worse than a messy fountain of sticky soft drink.


Since bleach is used extensively in a lot of household cleaning products – and if you're using a few cleaners for a better clean and deeper disinfection – there's a high chance the chemicals may cross paths.

(Photo: Pexels/Gustavo Fring)

Bleach can be labelled as sodium hypochlorite or chlorine-based bleaching agent on the container. It is found in a wide variety of household cleaning products, especially toilet bowl cleaners and laundry detergents, said Tan Mui Hua, a senior curriculum specialist at Science Centre Singapore’s STEM Inc.

And for good reasons, too. Not only can it sanitise surfaces, bleach can also decolourise stains “by oxidising the compounds that form stains”, said Tan. In laundry, the broken-down stains are more easily removed by the detergent and the mechanical action of the washing machine, she said.

READ: The next YouTube trend: Watching people clean their houses

But take note that bleach is "highly corrosive, reactive, and oxidising", said Phoon Chee Wee, a senior specialist in medicinal chemistry and senior lecturer with Nanyang Polytechnic's School of Applied Science.

"It can generate many toxic chemicals when mixed," he said. "The best option is always apply the cleaners first, then wash them away with water before any bleach application."

When bleach fumes mix with limonene, they may create tiny particles that may be damaging to both people’s and animals’ health.

Take, for instance, limonene, a chemical that gives many household cleaners a citrusy smell, said Johnson Zhuo, the managing director of Dream Sparkle, which offers commercial and residential cleaning services. 

“When bleach fumes mix with limonene, they may create tiny particles that may be damaging to both people’s and animals’ health", though, he added, more research is needed to determine how extensive the risks are.


If you can’t remember all the information in this article, remember this: Don’t mix bleach with ammonia, another commonly found chemical in household cleaners. For instance, don’t add bleach to a floor cleaner that uses ammonia.

When combined, bleach will react with ammonia to generate a variety of chloramines such as monochloramine, dichloramine and trichloramine, said Phoon. "Contact with high concentrations of the gases may cause skin, eye and respiratory tract irritation."

The other substance created is the flammable hydrazine, which “may cause irritation of the eyes, nose, throat, and could even damage the liver, kidneys and central nervous system”, said Tan.

(Photo: Pexels/Karolina Grabowska)

Ammonia can be found in window cleaners, furniture polish, drain cleaners, toilet cleaners, multi-surface cleaners, glass cleaners and stainless-steel cleaners, said Tan. It is particularly good for breaking down grime or stains from animal fats or vegetable oils, such as cooking grease and wine stains.

You’ll know that a cleaner contains ammonia when you find “ammonium hydroxide” or “aqua ammonia” on its label, said Zhuo. To prevent unintentional mixing, “always read the product label or manufacturer’s instructions before using it”.

Other than bleach and ammonia, here’s a look at other combinations to avoid:


Urine contains urea – and urea can be further broken down into ammonia. By applying bleach to the urine, you are creating the aforementioned chloramine gas.

A better bet: Clean the urine spillage with soap and water before using bleach for thorough disinfection. "Following which, simply remove the bleach with water," said Phoon.


For the same reason above, do not combine bleach or a bleach-based product with an ammonia-based cleaner in the toilet bowl. “Even at low levels, the chloramine gas can irritate the eyes, nose and throat, and cause coughing and breathing problems,” said Zhuo.

READ: House cleaning: How to disinfect the entire home to protect you from COVID-19

Don’t forget, bleach alone can be harmful to skin as well. “Peeing into a toilet bowl that still contains bleach could cause some of the bleach to splash up onto your skin. This can lead to skin irritation or burns,” Zhuo cautioned. 

A better bet: Apply the toilet bowl cleaner first, then clear it by flushing, recommended Phoon. "Ensure that there is no toilet cleaner left before using bleach for a thorough disinfection." Or just use white vinegar, suggested Tan. 

(Photo: Pexels/Karolina Grabowska)

Mould or mildew removers typically contain acid, said Zhuo. “If we mixed bleach with acid, it can form chlorine gas, which is a green and very noxious gas that can cause respiratory problems. It is very poisonous to breathe in.”

Another downside to using bleach on mould and mildew? It is only effective against them on non-porous materials such as coated tiles, bathtubs, glass and countertops, said Tan. 

A better bet: Use the mould or mildew remover first, and wash it away with water before using bleach for a thorough disinfection, said Phoon. Or simply use white vinegar, said Tan.


If the oven cleaner contains acid, it will react with the sodium hypochlorite in bleach to produce chlorine gas, warned Phoon.

A better bet: Baking soda is recommended, said Tan. You can mix baking soda with water. If you prefer to use an oven cleaner, make sure you clean it off with water first before using bleach for a thorough disinfection, said Phoon.

Peeing into a toilet bowl that still contains bleach could cause some of the bleach to splash up onto your skin.


Social media brims with "natural" DIY cleaning recipes that you can pre-mix ahead of time. And if you think you’d be safe pairing bleach with natural ingredients such as vinegar, lemon and baking soda, not quite.

It may also be worth noting that homemade cleaners may not be as effective as store-bought cleaning products, said Phoon. "Those who wish to use less chemicals may opt for soap and water instead, which will still disinfect surfaces as soap removes bacteria. Adding some lemon or lime slices can also aid in removing fishy smells," he said.

Here’s a look at what not to combine:

(Photo: Pexels/Karolina Grabowska)

Like the bleach and mould remover example above, pairing bleach with an acid such as vinegar or lemon juice releases the harmful chlorine gas, which can affect the mucous membranes in our body, causing watery eyes, chest congestion, burning sensation and skin irritation, according to Tan.


Unless you want to lose consciousness while doing household chores, don’t mix the two. You’ll release chloroform, which could knock a person out and cause organ damage, said Tan. “It may also cause irritation to the eyes, respiratory system and skin,” she said.

Rubbing alcohol – also known as isopropyl alcohol or isopropanol – can usually be found in oven and window cleaners, said Phoon, as well as disinfecting sprays and moist towelettes.

READ: Thinking of deep cleaning your home? Here’s what you need to look out for


There will be foaming, which can lead you to think you’re getting great cleaning properties. But sorry, it’s just a chemical reaction that results in mostly water, carbon dioxide and sodium acetate – harmless but useless for cleaning, said Tan.

“If stored in a closed container, the mixture may explode due to the pressure building up from the release of carbon dioxide gas in an enclosed space,” she warned.


Hydrogen peroxide can be found in multi-purpose sanitisers and kitchen cleaners, and has been hailed as the gentler disinfectant to bleach. 

But don’t get complacent with it. For instance, using hydrogen peroxide with vinegar can lead to the formation of the corrosive peracetic acid, which can irritate your skin, eyes, and respiratory system, said Tan.

Source: CNA/bk