Chlorhexidine

Chlorhexidine	Last updated: 06/09/2025
(Also known as: chlorohexidine)

GENERAL INFORMATION

Description

Chlorhexidine is an antiseptic, antibacterial agent and disinfectant active against both gram-positive and gram-negative microbes. It is usually formulated as the gluconate.

Examples of veterinary uses

Used mainly as a topical disinfectant cleanser for skin wounds and for ear and gum infections. It is also used to sterilize veterinary surgeries.

Examples of species treated

Cattle; Cats; Dogs

Approval status

VMR 2013/2033 approval status (GB/UK)

Approved

EU Regulatory approval status

Approved

Chemical structure

Isomerism

Chlorhexidine does not exhibit classical stereoisomerism like many chiral drugs, because its molecular structure lacks stereocentres. Instead, its isomerism is more structural in nature, related to the conformational flexibility of its bisbiguanide backbone. The molecule consists of two 4-chlorophenyl rings connected by a hexamethylene bridge, with biguanide groups on either end. This linear and symmetrical structure allows for rotational isomerism around the central chain, which can influence how the molecule interacts with microbial membranes. However, these conformers do not constitute distinct stereoisomers in the traditional sense.

Chemical formula

C₂₂H₃₀Cl₂N₁₀

Canonical SMILES

C1=CC(=CC=C1NC(=NC(=NCCCCCCN=C(N)N=C(N)NC2=CC=C(C=C2)Cl)N)N)Cl

Isomeric SMILES

C1=CC(=CC=C1N/C(=N/C(=NCCCCCCN=C(/N=C(/NC2=CC=C(C=C2)Cl)\N)N)N)/N)Cl

International Chemical Identifier key (InChIKey)

GHXZTYHSJHQHIJ-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C22H30Cl2N10/c23-15-5-9-17(10-6-15)31-21(27)33-19(25)29-13-3-1-2-4-14-30-20(26)34-22(28)32-18-11-7-16(24)8-12-18/h5-12H,1-4,13-14H2,(H5,25,27,29,31,33)(H5,26,28,30,32,34)

2D structure diagram/image available?

Yes

General status

Veterinary substance type

Antiseptic, Bactericide, Antimicrobial

Substance groups

Unclassified substance

Minimum active substance purity

Known relevant impurities

Substance origin

Synthetic

Mode of action

Disrupts the integrity of the cell membrane and causes the leakage of intracellular components of the organisms.

Molecular targets

[Bacterial cell membrane target; cationic bisbiguanide binder]

CAS RN

55-56-1

EC number

200-238-7

CIPAC number

US EPA chemical code

PubChem CID

9552079

Therapeutic Class

Dermatogiocals: Antiseptics and disinfectants

ATCvet Code

QD08AC52

Controlled Drug?

Regulation 37/2010 MRL Classification

Allowed substance (Table 1: All food producing species)

Molecular mass

505.45

PIN (Preferred Identification Name)

IUPAC name

(1E)-2-[6-[[amino-[(E)-[amino-(4-chloroanilino)methylidene]amino]methylidene]amino]hexyl]-1-[amino-(4-chloroanilino)methylidene]guanidine

CAS name

1,6-bis(5-(p-chlorophenyl)biguanidino)hexane

Forever chemical

Other status information

Relevant Environmental Water Quality Standards

Physical state

Colourless to pale yellow crystalline solid

Related substances & organisms

chlorhexidine gluconate

Commercial

Property

Value

Availability status

Current

Introduction & key dates

1953, introduced UK

Example manufacturers & suppliers of products using this active now or historically

Vet Way Ltd

Example products using this active

Vet-Hands Surgical Scrub
NVS Antimicrobial Skin
Chlorhex-Vet
Nolvasan
Hibitane Veterinary

Formulation and application details

Available as solutions for topical application

Commercial production

The production of chlorhexidine typically begins with the condensation of p-chloroaniline with cyanoguanidine to form a biguanide intermediate. This is followed by a reaction with hexamethylene diisocyanate or a similar linker to create the bisbiguanide structure that defines chlorhexidine. The process requires careful control of temperature, pH, and reaction time to ensure high yield and purity. Once synthesised, the crude product undergoes purification steps such as recrystallisation or solvent extraction to remove impurities. Depending on the intended formulation, like gluconate, acetate, or hydrochloride salt, the purified chlorhexidine base is then neutralised with the appropriate acid.

Impact on climate of production and use

Published GHG data is not available for most pharmaceuticals. However, according to industry, global averages suggest producing 1 kg of a typical active pharmaceutical ingredient can range from 10 to 100 kg CO₂e for small molecule drugs and potentially up to 1000 kg CO₂e for complex biologicals such as vaccines, depending on the drug type, its formulation, complexity of synthesis, solvent recovery, and energy sources used.

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

Solubility - In water at 20 °C (mg l⁻¹)

800

Moderate

Solubility - In organic solvents at 20 °C (mg l⁻¹)

Melting point (°C)

134

Boiling point (°C)

Degradation point (°C)

Flashpoint (°C)

Octanol-water partition coefficient at pH 7, 20 °C

1.20 X 10⁰⁰

Calculated

Log P

0.08

Low

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

1.07

Dissociation constant pKa) at 25 °C

10.78

at 25 °C

Vapour pressure at 20 °C (mPa)

2.64 X 10^-09

as acetate

Low volatility

Henry's law constant at 25 °C (Pa m³ mol⁻¹)

1.25e-25

as acetate

Non-volatile

Volatilisation as max % of applied dose lost

From plant surface

From soil surface

Maximum UV-vis absorption L mol⁻¹ cm⁻¹

Surface tension (mN m⁻¹)

Refractive Index

Environmental release

Degradation

Property

Value

Source; quality score; and other information

Interpretation

Soil degradation (days) (aerobic)

DT₅₀ (typical)

DT₅₀ (lab at 20 °C)

DT₅₀ (field)

DT₉₀ (lab at 20 °C)

DT₉₀ (field)

Note

Manure DT₅₀ (days)

Aqueous photolysis DT₅₀ (days) at pH 7

Value

Note

Aqueous hydrolysis DT₅₀ (days) at 20 °C and pH 7

Value

Note

Water-sediment DT₅₀ (days)

Water phase only DT₅₀ (days)

Sediment phase only DT₅₀ (days)

Air degradation

As this parameter is not normally measured directly, a surrogate measure is used: ‘Photochemical oxidative DT₅₀’. Where data is available, this can be found in the Fate Indices section below.

Decay in stored produce DT₅₀

Soil adsorption and mobility

Property

Value

Source; quality score; and other information

Interpretation

Linear

K_d (mL g⁻¹)

Non-mobile

K_oc (mL g⁻¹)

31600

Notes and range

Literature estimate

Freundlich

K_f (mL g⁻¹)

K_foc (mL g⁻¹)

¹/_n

Notes and range

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

Bio-concentration factor

BCF (l kg⁻¹)

CT₅₀ (days)

Known metabolites

None

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 1800

Mouse as the digluconate

Moderate

Mammals - Short term dietary NOEL

(mg kg⁻¹)

(ppm diet)

Mammals - Chronic 21d NOAEL (mg kg⁻¹ bw d⁻¹)

Birds - Acute LD₅₀ (mg kg⁻¹)

Birds - Short term dietary (LC₅₀/LD₅₀)

Birds - Chronic 21d NOEL (mg kg⁻¹ bw d⁻¹)

Earthworms - Acute 14 day LC₅₀ (mg kg⁻¹)

Earthworms - Chronic NOEC, reproduction (mg kg⁻¹)

Soil micro-organisms

Collembola

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

Non-target plants

Vegetative vigour ER₅₀ (g ha⁻¹)

Seedling emergence ER₅₀ (g ha⁻¹)

Honeybees (Apis spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Unknown mode acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Chronic

Notes

Bumblebees (Bombus spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Mason bees (Osmia spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Other bee species (1)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Other bee species (2)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Beneficial insects (Ladybirds)

Beneficial insects (Lacewings)

Beneficial insects (Parasitic wasps)

Beneficial insects (Predatory mites)

Beneficial insects (Ground beetles)

Aquatic ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Temperate Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

Temperate Freshwater Fish - Chronic 21 day NOEC (mg l⁻¹)

Tropical Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

> 1.4

Danio rerio

Moderate

Temperate Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

> 0.06

Daphnia magna as acetate

High

Temperate Freshwater Aquatic invertebrates - Chronic 21 day NOEC (mg l⁻¹)

Tropical Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

Aquatic crustaceans - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, static, water (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, sediment (mg kg⁻¹)

Aquatic Plants (free-floating, fonds growth, fresh) - 7 day (mg l⁻¹)

Aquatic plants (rooted, growth rate, fresh) - 14 day (mg l⁻¹)

Algae - Acute (growth rate, fresh; mg l⁻¹)

Algae - Chronic (growth rate, fresh; mg l⁻¹)

Mesocosm study data

NOEAEC mg l⁻¹

Marine bivalves

HUMAN HEALTH AND PROTECTION

General

Property

Value

Source; quality score; and other information

Interpretation

Threshold of Toxicological Concern (Cramer Class)

High (class III)

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 1800

Mouse as the digluconate

Moderate

Mammals - Dermal LD₅₀ (mg kg⁻¹ body weight)

500

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

> 2.03

Rat

Other Mammal toxicity endpoints

Subcutaneous LD₅₀ = 1000 mg kg⁻¹

Rat

Intraperitoneal LD₅₀ = 60 mg kg⁻¹

Rat

ADI - Acceptable Daily Intake (mg kg⁻¹ bw day⁻¹)

ARfD - Acute Reference Dose (mg kg⁻¹ bw day⁻¹)

AAOEL - Acute Acceptable Operator Exposure Level (mg kg⁻¹ bw day⁻¹)

AOEL - Acceptable Operator Exposure Level - Systemic (mg kg⁻¹ bw day⁻¹)

Dermal penetration studies (%)

Dangerous Substances Directive 76/464

Exposure Routes

Public

Occupational

Mammalian dose elimination route and rate

Excretion is primarily through the faeces (~ 90%). Also found in breast milk.

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

No data found

; ; ; ;

No data found

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

No data found

Respiratory tract irritant

Skin irritant

Skin sensitiser

Eye irritant

Phototoxicant

No data found

General human health issues

No further information available

Handling issues

Property

Value and interpretation

General

May decompose on heating emiting dangerous gaseous substances - halogenated compounds, oxides of nitrogen
IMDG Transport Hazard Class 9

CLP classification 2013

WHO Classification

Not listed (Not listed)

UN Number

UN3077

Waste disposal & packaging

Packaging Group III (minor danger)

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

chlorhexidine

French

German

Danish

Italian

Spanish

clorhexidina

Greek

Polish

Swedish

Hungarian

Dutch

Norwegian

Record last updated:	06/09/2025
Contact:	aeru@herts.ac.uk
Please cite as:	Lewis, K.A., Tzilivakis, J., Warner, D. and Green, A. (2016) An international database for pesticide risk assessments and management. Human and Ecological Risk Assessment: An International Journal, 22(4), 1050-1064. DOI: 10.1080/10807039.2015.1133242