Guidance

Chlorine: general information

Updated 3 September 2024

Overview

Chlorine is a reactive gas that is approximately three times as heavy as air and has a characteristic odour similar to bleach. It is part of the group of chemicals called ‘halogens’ which include fluorine, bromine, and iodine. The word chlorine comes from the Greek word for ‘pale green’, the colour of chlorine gas.

Chlorine does not naturally exist as a gas as it is too reactive. Instead, it reacts with other earth elements to form halogen salts. For example, common salt sodium chlorate (also known as sea salt or ‘halite’) is a combination of sodium and chlorine.

Uses of chlorine

Chlorine is an important industrial chemical, used to make other chemicals such as plastics. Perhaps one of the most important applications of chlorine is in the disinfection of public water supplies to prevent the transmission of waterborne diseases such as cholera and typhoid. The introduction of chlorinated water supplies has helped to eradicate such diseases from the developed world. Chlorine based chemicals are used to disinfect swimming pools. Chlorine is used in the pulp and paper industry as a bleaching agent and chlorine-based chemicals are also present in many domestic cleaning products.

Chlorine was used as a chemical warfare agent during World War I.

How chlorine gets into the environment

Chlorine is a reactive chemical and as such does not normally exist in its gaseous form in the environment. The most likely cause of chlorine in the environment is following accidental release from an industrial site or transport vehicle.

Exposure to chlorine

Chlorine is a gas and so the eyes and lungs are most likely to be exposed. It may also be transported in liquid form. Products which contain or release chlorine which are stored at home should be kept out of the reach of children and in an appropriate container. Individuals may be exposed to gases formed by the inappropriate mixing of cleaning products.

Exposure to chlorine gas may occur if it is used, stored, or manufactured in the workplace. However, safe limits are enforced to protect the employees - such levels are below those that are thought to cause harmful effects.

How exposure to chlorine can affect your health

The presence of chlorine in the environment does not always lead to exposure. In order for it to cause any adverse health effects you must come into contact with it. You may be exposed to chlorine by breathing it or by skin or eye contact with it. Following exposure to any chemical, the adverse health effects you may encounter depend on several factors, including the amount to which you are exposed (dose), the way you are exposed, the duration of exposure, the form of the chemical and if you were exposed to any other chemicals.

Minor exposures may result in a burning sensation of the eyes and throat. More substantial exposure may cause coughing or breathing difficulties. Exposure to high concentrations of chlorine gas can damage the lungs and airways. This may cause a build-up of fluid in the lungs which can be fatal. Following severe injuries from inhaling chlorine, there may be a lasting effect on the lungs and airways. However, most people who develop symptoms of poisoning following exposure to chlorine will not suffer any long-term effects.

Exposure to liquid or gaseous chlorine may cause irritation and burns to the skin and eyes.

Chlorine and cancer

Exposure to chlorine has not been linked to the development of cancer. In other words, chlorine is not thought to be carcinogenic.

Vulnerable groups

Individuals with existing problems of the lungs and airways (including asthma, hay fever, and chronic bronchitis) and heavy smokers may be more sensitive to the effects of chlorine gas. A small proportion of individuals may acquire a long-term sensitivity to inhaled chemicals known as ‘reactive airways dysfunction syndrome’ or RADS.

Pregnancy and the unborn child

There are limited data available on the effects of chlorine exposure on pregnancy and the unborn child.

Normal use of household products containing chlorine, or the use of swimming pools would not be expected to cause harm to the unborn child.

Children

Children are expected to be affected by chlorine in the same way as adults. Household products that contain chlorine should be stored in appropriate containers and kept out of the reach of children.

What to do if you are exposed to chlorine

You should remove yourself from the source of exposure. If you have inhaled chlorine, seek medical advice.

If you have got chlorine on your skin, remove soiled clothing, wash the affected area with lukewarm water and soap for at least 10 to 15 minutes and seek medical advice.

If you have got chlorine in your eyes, remove contact lenses, irrigate the affected eye with lukewarm water for at least 10 to 15 minutes and seek medical advice.

Additional sources of information

NHS Choices - Poisoning

UKTIS - Best Use of Medicines in Pregnancy

The information contained in this document from the UKHSA Radiation, Chemicals and Environment Directorate is correct at the time of its publication.

Email chemcompendium@ukhsa.gov.uk if you have any questions about this guidance or enquiries@ukhsa.gov.uk if you have any other questions.