The one-stop guide to working with irritants: from hazard classification to mitigating risks

What are irritants?

Chemical irritants are substances/mixtures that may cause: (i) reversible irritation upon contact with the skin or eyes, (ii) allergic reactions (e.g. allergic contact dermatitis, irritant contact dermatitis), (iii) acute toxicity leading to serious adverse health effects, (iv) transient respiratory irritation or narcotic effects (drowsiness, dizziness), or (v) damage to the ozone layer.

Many irritants have multiple hazards associated with it. Dichloromethane for instance is both an irritant and a carcinogen (represented by the ‘health hazard’ pictogram). Moreover, common solvents such as acetone and ethanol are both flammable irritants.

The nature of the chemical, concentration, duration, frequency of exposure, and mode of exposure affects the severity of symptoms.

The ‘exclamation mark’ pictogram is used to represent 5 health and one environmental GHS hazard classes

Hazard Class


Signal Word

Hazard Statement

Hazard Code

Acute toxicity


Category 4

Acute toxicity estimate (ATE) is derived from available LD50 and LC50 data.

(i) Oral (mg/kg bodyweight)

300 < ATE ≤ 2000


Harmful if swallowed


(ii) Dermal (mg/kg bodyweight)

1000 < ATE ≤ 2000


Harmful in contact with skin


(iii) Inhalation (parts per million per volume (ppmV))

2500 < ATE ≤ 20000


Harmful if inhaled


(iv) Vapours (mg/l)

10.0 < ATE ≤ 20.0


Harmful if inhaled


(v) Dusts and mists (mg/l)

1.0 < ATE ≤ 5.0


Harmful if inhaled


Skin corrosion/ irritation


Category 2

(i) Mean score of ≥ 2.3 and ≤ 4.0 for erythema/eschar or for oedema in at least 2 of 3 tested animals from gradings at 24, 48, and 72 hours after patch removal or from grades on 3 consecutive days (if reactions are delayed) after the onset of skin reactions; or (ii) inflammation (including alopecia, hyperkeratosis, hyperplasia, and scaling) that persists to the end of a 14 day observation period in at least 2 animals; or (iii) very definite positive effects related to chemical exposure in a single animal but less than the criteria above.


Causes skin irritation


Category 3 (no pictogram)

Applies to some authorities only.

Mean score of ≥ 1.5 and < 2.3 for erythema/eschar or for oedema in at least 2 of 3 tested animals from gradings at 24, 48 and 72 hours or from grades on 3 consecutive days (if reactions are delayed) after the onset of skin reactions (when not included in Category 2).


Causes mild skin irritation


Serious eye damage/eye irritation

Category 2/2A

Substances that produce in at least 2 of 3 tested animals a positive response (fully reversed within a 21-day observation period) of: (i) corneal opacity ≥ 1; and/or (ii) iritis ≥ 1; and/or (iii) conjunctival redness ≥ 2; and/or (iv) conjunctival oedema (chemosis) ≥ 2.


Causes serious eye irritation


Category 2B (no pictogram)

When the effects listed in Category 2A are fully reversible within 7 days of observation.



Causes eye irritation


Skin Sensitization

Category 1

Evidence of skin sensitization in a substantial number of persons, or if there are positive results from an appropriate animal test.


May cause an allergic skin reaction


(i) 1A

Showing a high frequency of occurrence in humans and/or a high potency in animals, presumed to produce significant sensitization in humans. Severity of reaction may also be considered.


May cause an allergic skin reaction


(ii) 2B

Showing a low to moderate frequency of occurrence in humans and/or a low to moderate potency in animals, presumed to produce sensitization in humans. Severity of reaction may also be considered.



May cause an allergic skin reaction


Specific target organ toxicity- single exposure

Category 3

Substances or mixtures that transiently alter human function after exposure, and from which humans may recover in a reasonable period without significant alteration of structure or function.



May cause respiratory irritation or

may cause drowsiness or dizziness




Hazardous to the ozone layer

Category 1

Any of the controlled substances listed in the Annexes of the Montreal Protocol; or any mixture containing at least one ingredient listed in the Annexes at a concentration ≥ 0.1 %.



Harms public health and the environment by destroying ozone in the upper atmosphere




How to mitigate the risks of working with irritants 

1. Receiving:
  • Only order and store the minimal amount required for your laboratory.
  • Be aware of multiple associated hazards such as corrosive bases or flammable solvents, which are also irritants.
  • Use a lab management program to keep track of inventory.
2. Storage:
  • Ensure appropriate ventilation in areas where irritants are stored or handled and do not work with irritants in facilities with a recirculating exhaust system.
  • Include legible labels with hazard information and GHS symbols on all containers.
  • Store irritants away from incompatible chemicals, heat sources, direct sunlight, and high-traffic areas.

3. Handling:

  • Perform all necessary training before working with irritants: depending on the chemical, additional safety and handling certifications may be required.
  • Wear appropriate PPE: gloves, lab coats and goggles, as well as consider tight chemical splash goggles, chemical resistant gloves, disposable lab coats, and/or respirators or face masks.
  • Perform all work with irritants in a fume hood, biosafety cabinet, or filtering workstation.
  • Do not dispense volatile irritant chemicals directly onto a balance in the general lab space. Instead, in a fume hood place material in a pre-tared sealable container and adjust the amount inside the container until the desired mass is reached.
  • Do not work with irritants if you are alone; ensure a colleague is nearby in case of an emergency.
  • Use disposable bench protectors in areas where irritants are handled if possible.
4. Health and environmental considerations:
  • Take extra precautions if you have any personal health issues. For example, those with asthma may be especially susceptible to respiratory irritants.
  • Account for your environment: a humid or hot working environment may cause sweating, allowing chemicals to be more readily absorbed into the skin.
  • Take precautions to avoid irritants outside of the lab such as at-home cleaning products, which will reduce low dosage long term exposure.
5. Emergencies and spills:
  • Ensure emergency irrigation such as safety showers and eyewash stations are operational and within a 10-second travel distance of where irritants are being handled.
  • In case of spills, immediately clean the area if possible, and wash your hands with soap and water.
  • Equip the laboratory with first aid supplies such as bandages, compresses, creams, and ointments for the treatment of chemical burns.

 6. Alternatives:

  • Examine your SOP to determine if substitutions for less hazardous chemicals can be used.
  • If substitutions are not possible, determine if changing the form of the chemical is possible. Solid pellets for example are generally less irritating than fine powders.
  • Automate your process to reduce your exposure to these chemicals, especially if tasks are repetitive.
7. Waste:
  • Appropriately separate incompatible irritant waste. For example, store acids and bases separately.
  • Avoid storing irritant waste for long periods of time.
By shuhan yang


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