Hydrochloric Acid (Spirits of Salt, Muriatic Acid)

What is hydrochloric acid and what is it used for?

Hydrochloric acid is a solution of hydrogen chloride gas in water. It is also present, in very diluted form, in the digestive juices in our stomachs; but the concentrations in cleaning products are very different.

What makes it useful for cleaning is that it quickly dissolves limescale (calcium carbonate), rust and mineral deposits. It is used to remove thick layers of limescale from toilets, sinks and tile grout. The same strength also makes it corrosive to skin, eyes and many surfaces.

Which products contain it?

• Spirits of salt (a straight hydrochloric acid solution)
• Some strong descalers and bathroom cleaners
• Some acidic toilet and toilet bowl cleaners
• Industrial rust removers and metal cleaners

On the label it appears as “hydrochloric acid” or “HCl”. The packaging usually carries the corrosive substance pictogram and a “do not mix with bleach” warning.

Is it harmful? The scientific assessment

Under the EU CLP classification, concentrated hydrochloric acid causes severe skin burns and eye damage (H314), may cause respiratory irritation (H335) and may be corrosive to metals (H290). The sharp fumes rising from an open bottle can cause coughing and a burning throat, especially when used with hot water or in an enclosed space.

The acid does not build up permanently in the body and is not classified as a carcinogen; the risk is entirely acute, that is, linked to the moment of contact. Splashes in the eyes are among the most serious accidents because they can cause permanent damage.

Be careful with surfaces too: it dissolves marble, travertine and natural stone, and it can corrode chrome plating, aluminium and some grouts.

The most important warning: don't mix it with bleach

When hydrochloric acid or an acidic descaler mixes with bleach containing sodium hypochlorite, chlorine gas is released. Chlorine gas causes severe coughing, a burning feeling in the chest, shortness of breath and watering eyes; high exposure can lead to lung damage. Pouring bleach into the toilet and then adding hydrochloric acid is the most common scenario for these accidents.

• Always use hydrochloric acid on its own and, if it needs diluting, add the acid to the water (not the other way round).
• Wear thick rubber gloves and, if possible, eye protection; open the windows.
• Rinse the surface thoroughly with water after use; leave no residue before switching to another product.

What to do in case of exposure

If you have inhaled fumes or gas, get to fresh air immediately. If it splashes into the eyes, rinse the eye under plenty of running water for at least 15 minutes and get medical help. If it comes into contact with the skin, rinse with plenty of water. If swallowed, do not try to induce vomiting. Call your local poison control centre (in Türkiye: UZEM, 114); for severe symptoms, call 112.

What to do when you see it on a label

Everyday limescale cleaning usually does not need an acid as strong as hydrochloric acid. For light to moderate limescale, products based on citric acid or vinegar are often enough and do less harm in an accident. If you do use hydrochloric acid, store it in its original container out of children's reach; never decant it into a water bottle. Remember: citric acid and vinegar are acids too; they must not be mixed with bleach either.