Sodium Hypochlorite (Bleach)

What is sodium hypochlorite and what does it do?

Sodium hypochlorite is a chlorine-containing salt that acts as a powerful oxidising agent when dissolved in water. It inactivates bacteria, viruses and fungi by disrupting their cell structure, and it bleaches by breaking down the dye molecules in coloured stains.

Because it is cheap, fast-acting and broad-spectrum, it is widely used both in homes and in areas such as hospitals and water treatment. Its characteristic "swimming pool smell" also comes from this substance and the organic dirt it reacts with.

Which products contain it?

• Bleach (regular, thick, scented)
• Chlorine-based surface and bathroom sprays, mould removers
• Some gel toilet cleaners and gel drain unblockers
• Chlorine laundry bleaches and some dishwasher products

On the label it appears as "sodium hypochlorite", "active chlorine" or "chlorine-based bleach". The packaging usually carries the warning "Warning! Do not use together with other products. May release dangerous gases (chlorine)" (EUH206).

Is it harmful? The scientific assessment

Under EU CLP classification, concentrated sodium hypochlorite solutions cause severe skin burns and eye damage (H314) and are very toxic to aquatic life (H400/H410). They also carry the warning "contact with acids liberates toxic gas" (EUH031). Because the substance is diluted in household products, these are mostly labelled at the level of skin and eye irritation; even so, a splash in the eye is a serious matter.

When used heavily in an enclosed, poorly ventilated space, its fumes can irritate the nose, throat and eyes, and in people with asthma it can trigger coughing and shortness of breath. Because it reacts with organic matter in water to form small amounts of chlorinated by-products, it is also recommended not to use more than necessary for environmental reasons.

Sodium hypochlorite is not classified by the IARC as carcinogenic to humans. The main risk is acute poisoning caused by the wrong mixtures.

The most important warning: never mix

• Bleach + acid (hydrochloric acid, descaler, vinegar, acidic toilet cleaner): releases chlorine gas. This can cause severe coughing, a burning feeling in the chest and shortness of breath, and in serious cases lung damage.
• Bleach + ammonia (some glass cleaners, urine residue): chloramine gases form; these cause similar respiratory symptoms.
• Bleach + alcohol or other cleaners: unpredictable reactions can occur; using one product and rinsing thoroughly is the safest approach.

Mixing products "so that they clean better" does not increase the effect; it only creates a risk of toxic gas. When switching products, rinse the surface with plenty of water.

What to do in case of exposure

• If you have inhaled gas, leave the area immediately, get to fresh air and open the windows.
• If it splashes into the eyes, rinse them with plenty of running water for at least 15 minutes.
• If it spills on the skin, rinse with plenty of water and remove wet clothing.
• If swallowed, do not try to induce vomiting.
• In all cases, call your local poison control centre (in Türkiye: UZEM, 114) to find out what to do; for severe symptoms such as shortness of breath, call 112.

What to do when you see it on a label

Dilute bleach at the ratio recommended on the packaging, wear gloves and ventilate the room. Store it in its original container, out of children's reach. In everyday cleaning, there is no need to disinfect every surface; for most dirt, water with detergent is enough. If you want a chlorine-free option for whitening, consider oxygen bleaches containing sodium percarbonate.