PUBLIC HEALTH STATEMENT

 Chlorine

Division of Toxicology and Environmental Medicine November 2010

______________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry

www.atsdr.cdc.gov/ Telephone: 1-800-232-4636 Fax: 770-488-4178 E-Mail: cdcinfo@cdc.gov

This Public Health Statement is the summary chapter from the Toxicological Profile for 

Chlorine. It is one in a series of Public Health Statements about hazardous substances and their 

health effects. A shorter version, the ToxFAQsTM, is also available. This information is 

important because this substance may harm you. The effects of exposure to any hazardous 

substance depend on the dose, the duration, how you are exposed, personal traits and habits, and 

whether other chemicals are present. For more information, call the ATSDR Information Center

at 1-800-232-4636.

____________________________________________________________________________________

This public health statement tells you about chlorine and the effects of exposure to it.

The Environmental Protection Agency (EPA) identifies the most serious hazardous waste sites in 

the nation. These sites are then placed on the National Priorities List (NPL) and are targeted for 

long-term federal clean-up activities. Chlorine gas is too reactive to be detected in 

environmental media at hazardous waste sites. Any chlorine gas released at these sites would be 

quickly converted to other substances whose primary source may or may not have been chlorine.

When a substance is released either from a large area, such as an industrial plant, or from a 

container, such as a drum or bottle, it enters the environment. Such a release does not always 

lead to exposure. You can be exposed to a substance only when you come in contact with it. 

You may be exposed by breathing, eating, or drinking the substance, or by skin contact. Since 

chlorine is highly reactive, you are unlikely to be exposed directly to it unless there has been a 

large scale accidental release nearby.

If you are exposed to chlorine, many factors will determine whether you will be harmed. These 

factors include the dose (how much), the duration (how long), and how you come in contact with 

it. You must also consider any other chemicals you are exposed to and your age, sex, diet, 

family traits, lifestyle, and state of health.
 PUBLIC HEALTH STATEMENT

 Chlorine

Division of Toxicology and Environmental Medicine November 2010

______________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry

www.atsdr.cdc.gov/ Telephone: 1-800-232-4636 Fax: 770-488-4178 E-Mail: cdcinfo@cdc.gov

1.1 WHAT IS CHLORINE?

Chlorine is a gas 

with a very 

irritating odor 

It is very unstable and quickly reacts with many substances to form other 

chemicals. 

Used in 

manufacturing 

and water 

disinfection 

Chlorine is an extremely important industrial chemical that is used in the 

production of thousands of products. 

It is also used for water disinfection, although the chlorine itself is quickly 

transformed into other chemicals at the beginning of the process.

Chlorine gas is 

not present in 

chlorinated water

A common misconception is that molecular chlorine (Cl2) is present in 

chlorinated water. During water chlorination, molecular chlorine gas may be 

added to the water at first; however, the chlorine is quickly transformed into

other chemicals, which actually disinfect the water. Hypochlorous acid and 

hypochlorite anion are two of these chemicals that disinfect the water.

The terms “free chlorine” and “aqueous chlorine” in drinking water usually 

refers to the amount of hypochlorous acid and hypochlorite in the water. It is 

important to recognize that these compounds are different from molecular 

chlorine.

 

Bleach is not 

chlorine

One of the important products that chlorine is used to make is bleach, and 

people sometimes confuse chlorine with bleach. Bleach contains a 

compound called sodium hypochlorite. If you mix acidic chemicals with 

bleach, chlorine can be formed and given off as a gas.

1.2 WHAT HAPPENS TO CHLORINE WHEN IT ENTERS THE ENVIRONMENT?

Chlorine is very 

unstable in the 

environment

Chlorine is very unstable, and reacts with a variety of chemicals and water 

when it is released into the environment. 

Rapidly broken 

down

• Air

• Water

Chlorine is broken down by sunlight within minutes.

Chlorine dissolves in water and is converted into chloride and hypochlorous 

acid. 
 PUBLIC HEALTH STATEMENT

 Chlorine

Division of Toxicology and Environmental Medicine November 2010

______________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry

www.atsdr.cdc.gov/ Telephone: 1-800-232-4636 Fax: 770-488-4178 E-Mail: cdcinfo@cdc.gov

Chlorine can 

travel far from its 

source

If chlorine is spilled into water or onto soil or if it is released from a tank into 

the air, the chlorine will evaporate very quickly forming a greenish-yellow 

cloud that can be carried away from the source by the wind.

1.3 HOW MIGHT I BE EXPOSED TO CHLORINE?

Most people are 

not expected to 

be exposed to 

chlorine

Because chlorine is so reactive, it is not normally detected in the 

environment except for very low levels in the air above seawater. 

Accidental 

exposure to 

chlorine 

If an accident involving chlorine takes place nearby, such as a liquid chlorine 

spill, a leak from a chlorine tank, or a leak from a facility that produces or 

uses chlorine, you may be exposed through breathing and skin and eye 

contact.

You may also be exposed to chlorine if you mix household chemicals such 

as toilet cleaner with bleach. 

Hypochlorous acid is used to treat swimming pool water. You may be 

exposed to chlorine gas through the improper use of swimming pool 

chemicals.

Workplace air People who work in places where chlorine is made or used may be exposed 

to low levels over a period of time. 

People may be exposed to high levels if a large amount of chlorine is 

released during an accident.

1.4 HOW CAN CHLORINE ENTER AND LEAVE MY BODY?

Chlorine gas 

enters your body 

only when you 

breathe it in. 

Chlorine gas can enter your body through your nose or your mouth. 

At low concentrations (less than 10 ppm), almost all of the chlorine is 

removed from the air in the upper part of the respiratory airways and only a 

very small amount may reach your lungs.

If you drink hypochlorite solution, it may react with the acids in your 

stomach and possibly form chlorine gas.

 
 PUBLIC HEALTH STATEMENT

 Chlorine

Division of Toxicology and Environmental Medicine November 2010

______________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry

www.atsdr.cdc.gov/ Telephone: 1-800-232-4636 Fax: 770-488-4178 E-Mail: cdcinfo@cdc.gov

Immediately 

reacts with other 

chemicals

Chlorine gas reacts with the water in the cells located in the surface of the 

respiratory airways and forms other compounds that produce irritation of the 

airways. 

Most of these compounds eventually are transformed into chloride ions, 

which are normal components of the body.

1.5 HOW CAN CHLORINE AFFECT MY HEALTH?

This section looks at studies concerning potential health effects in animal and human studies.

Short-term 

exposure to 

chlorine in air

The following effects have been observed in humans briefly exposed to 

chlorine: 

• mild nose irritation at 1–3 ppm 

• eye irritation at 5 ppm

• throat irritation at 5–15 ppm 

• immediate chest pain, vomiting, changes in breathing rate, and 

cough at 30 ppm

• lung injury (toxic pneumonitis) and pulmonary edema (fluid in the 

lungs) at 40–60 ppm

• death after 30 minute exposure to 430 ppm

• death after a few minutes exposure to 1,000 ppm 

The concentrations listed above are approximate; the effects will depend 

also on exposure duration. In general, people who suffer from respiratory 

conditions such as allergies or hay fever, or who are heavy smokers, tend to 

experience more severe effects than healthy subjects or nonsmokers.

 

Long-term 

exposure to 

chlorine in air

No significant harmful health effects were observed in workers exposed for 

years to relatively low concentrations of chlorine (around 1 ppm).

The tissues inside the nose were principally affected in animals exposed to 

chlorine for longer durations.

Short-term 

exposure to 

hypochlorite 

solution by 

ingestion

Drinking small amounts of hypochlorite solution (less than a cup) can 

produce irritation of the esophagus. Drinking concentrated hypochlorite 

solution can produce severe damage to the upper digestive tract and even 

death. These effects are most likely caused by the caustic nature of the 

hypochlorite solution and not from exposure to molecular chlorine.
 PUBLIC HEALTH STATEMENT

 Chlorine

Division of Toxicology and Environmental Medicine November 2010

______________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry

www.atsdr.cdc.gov/ Telephone: 1-800-232-4636 Fax: 770-488-4178 E-Mail: cdcinfo@cdc.gov

Long-term 

exposure to 

hypochlorite 

solution by 

ingestion

There is no information on long-term ingestion of hypochlorite solution in 

humans. Animals that drank hypochlorite solution in water for up to 2 years 

did not show any significant health effects. The amount of hypochlorite 

solution in the water that the animals drank was much smaller than what is 

found in household bleach.

Skin exposure to 

hypochlorite 

solution

Spilling hypochlorite solution on the skin can produce irritation. The severity 

of the effects depends on the concentration of sodium hypochlorite in the 

bleach.

1.6 HOW CAN CHLORINE AFFECT CHILDREN?

This section discusses potential health effects in humans from exposures during the period from 

conception to maturity at 18 years of age.

Children are likely 

to have similar 

effects as adults, 

but may be more 

sensitive than 

adults

Short-term exposures (minutes) to high concentrations of chlorine affect 

children in the same manner they affect adults (i.e., mucous membrane and 

respiratory tract irritation). We do not know what the effects could be in 

children following longer-term (weeks or longer), low-level exposure to 

chlorine gas, but this type of exposure occurs only in workers and is not 

relevant to children. We also do not know what the effects could be in 

children following longer-term, low-level exposure to hypochlorite solution.

Birth defects We do not know whether exposure to chlorine gas during pregnancy can 

result in damage to unborn babies because there are no studies of pregnant 

women or pregnant animals exposed to chlorine gas. 

One study of rats exposed to hypochlorite solution during pregnancy found 

no evidence of birth defects or any other developmental alteration in the 

baby rats. The amount of chlorine that the rats consumed was many times 

higher than what people are normally exposed to through drinking water.

1.7 HOW CAN FAMILIES REDUCE THE RISK OF EXPOSURE TO CHLORINE?

Do not mix bleach 

with household 

cleaners 

Chlorine gas can be released to the air when bleach is mixed with other 

cleaning solutions that contain an acid; for example, some toilet cleaners. 

Mixing bleach with ammonia also produces very hazardous gases, such as 

chloramines.
 PUBLIC HEALTH STATEMENT

 Chlorine

Division of Toxicology and Environmental Medicine November 2010

______________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry

www.atsdr.cdc.gov/ Telephone: 1-800-232-4636 Fax: 770-488-4178 E-Mail: cdcinfo@cdc.gov

Store household 

chemicals out of 

reach of young 

children

Always store household chemicals in their original labeled containers out of 

reach of young children to prevent accidental poisonings. Never store 

household chemicals in containers children would find attractive to eat or 

drink from, such as old soda bottles. 

Follow 

instructions for 

swimming pool 

disinfection

Chlorine gas can also be released to the air when chemicals used to 

chlorinate swimming pools are mishandled. If you have a swimming pool at 

home, read the labels of the chlorination products carefully and do not let 

children play with these products. 

 

1.8 IS THERE A MEDICAL TEST TO DETERMINE WHETHER I HAVE BEEN 

EXPOSED TO CHLORINE?

There are no 

medical tests 

available for 

chlorine

There are no medical tests to determine whether you have been exposed 

specifically to chlorine. 

Chlorine is transformed in the body into chloride ions, which are normal 

components of the body. An enormous amount of chlorine has to be 

inhaled or ingested in order to detect a significant increase in chloride ions 

in the blood. This has occurred in a few cases of ingestion of large 

amounts of hypochlorite solution and one of them was a fatal case. 

1.9 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT MADE TO 

PROTECT HUMAN HEALTH?

The federal government develops regulations and recommendations to protect public health. 

Regulations can be enforced by law. The EPA, the Occupational Safety and Health 

Administration (OSHA), and the Food and Drug Administration (FDA) are some federal 

agencies that develop regulations for toxic substances. Recommendations provide valuable 

guidelines to protect public health, but cannot be enforced by law. The Agency for Toxic 

Substances and Disease Registry (ATSDR) and the National Institute for Occupational Safety 

and Health (NIOSH) are two federal organizations that develop recommendations for toxic 

substances.
 PUBLIC HEALTH STATEMENT

 Chlorine

Division of Toxicology and Environmental Medicine November 2010

______________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry

www.atsdr.cdc.gov/ Telephone: 1-800-232-4636 Fax: 770-488-4178 E-Mail: cdcinfo@cdc.gov

Regulations and recommendations can be expressed as “not-to-exceed” levels, that is, levels of a 

toxic substance in air, water, soil, or food that do not exceed a critical value that is usually based 

on levels that affect animals; they are then adjusted to levels that will help protect humans. 

Sometimes these not-to-exceed levels differ among federal organizations because they used 

different exposure times (an 8-hour workday or a 24-hour day), different animal studies, or other 

factors.

Recommendations and regulations are also updated periodically as more information becomes 

available. For the most current information, check with the federal agency or organization that 

provides it.

Some regulations and recommendations for chlorine include the following:

Levels in air set 

by EPA

EPA established an environmental air limit of 0.5 ppm. Exposure to higher 

levels could result in discomfort and irritation. Dependent on the 

concentration, these effects may be reversible when exposure ends.

Levels in 

workplace air set 

by OSHA

OSHA set a legal limit of 1 ppm chlorine in air as a ceiling limit. At no time 

should a worker’s exposure exceed this limit. 

Levels in drinking 

water set by EPA

EPA established a maximum contaminant level (MCL) and maximum

residual disinfectant level (MRDL) of 4 mg/L for free chlorine in drinking 

water.

1.10 WHERE CAN I GET MORE INFORMATION?

If you have any more questions or concerns, please contact your community or state health or 

environmental quality department, or contact ATSDR at the address and phone number below.
 PUBLIC HEALTH STATEMENT

 Chlorine

Division of Toxicology and Environmental Medicine November 2010

______________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry

www.atsdr.cdc.gov/ Telephone: 1-800-232-4636 Fax: 770-488-4178 E-Mail: cdcinfo@cdc.gov

ATSDR can also tell you the location of occupational and environmental health clinics. These 

clinics specialize in recognizing, evaluating, and treating illnesses that result from exposure to 

hazardous substances.

Toxicological profiles are also available on-line at www.atsdr.cdc.gov and on CD-ROM. You 

may request a copy of the ATSDR ToxProfilesTM CD-ROM by calling the toll-free information 

and technical assistance number at 1-800-CDCINFO (1-800-232-4636), by e-mail at 

cdcinfo@cdc.gov, or by writing to: 

Agency for Toxic Substances and Disease Registry

Division of Toxicology and Environmental Medicine

1600 Clifton Road NE

Mailstop F-62

Atlanta, GA 30333

Fax: 1-770-488-4178

Organizations for-profit may request copies of final Toxicological Profiles from the following:

National Technical Information Service (NTIS)

5285 Port Royal Road

Springfield, VA 22161

Phone: 1-800-553-6847 or 1-703-605-6000

Web site: http://www.ntis.gov/