What are they?

A respiratory sensitizer is a substance whose inhalation may cause hypersensitivity of the respiratory tract.

A skin sensitizer is a substance that may cause an allergic reaction following skin contact.

Sensitization comprises two phases. The first is the induction of a specific immune memory following exposure to an allergen. The second phase, known as elicitation, occurs when subsequent exposure to the substance causes an allergic response in a previously sensitized person.

In general, the exposure that triggers a reaction in a person who is already sensitized may be lower than that required to cause the initial sensitization.

Reactions may affect the skin and the respiratory system. Reported manifestations include allergic contact dermatitis, rhinitis, asthma and other respiratory symptoms. The INSST information on chemical risks specifically covers these two categories of sensitizers and identifies them by hazard statements H317 and H334.

Once sensitization has occurred, further exposure may cause allergic reactions. Prevention should therefore primarily aim to avoid or minimize exposure.

In the Occupational Exposure Limits for Chemical Agents in Spain 2026, agents capable of causing sensitization are identified with the notation “Sen”. The INSST states that this notation may also apply to agents that have sensitizing effects even if they are not specifically covered by the regulations on the classification of hazardous substances. It also warns that an OEL based on sensitization does not guarantee protection for people who are already sensitized.

Occupational Exposure Limits for Chemical Agents in Spain 2026 — INSST

What should be done?

Exposure to sensitizing substances should be avoided or minimized by applying the principles of prevention.

The first option should be to avoid using the substance or to replace it with another substance or process presenting a lower risk, whenever technically possible. If substitution is not possible, technical and organizational measures should be implemented to prevent or reduce exposure.

Preventive measures may include:

1. reducing to a minimum the quantities of sensitizing substances present in the workplace;
2. preventing or reducing their release into the working environment;
3. using closed systems or procedures that reduce direct contact and dispersion;
4. using ventilation and other collective protection measures, preferably at source;
5. reducing to a minimum the number of people exposed and the duration and intensity of exposure;
6. establishing appropriate hygiene and cleaning measures;
7. providing information and training on the risks and preventive measures;
8. using personal protective equipment when the above measures are insufficient and exposure cannot be avoided by other means.

Royal Decree 374/2001 establishes this preventive hierarchy and expressly states that substitution should be preferred whenever possible; personal protective equipment should be used when the previous measures are insufficient.

Workers must have access to information on the substances present, their risks, applicable occupational exposure limits and prevention and protection measures, as well as access to safety data sheets.

In the event of symptoms compatible with sensitization, the situation should be reported and an assessment should be requested from the appropriate health services. Where the risk assessment identifies a risk to health, Royal Decree 374/2001 provides for health surveillance under the conditions established in Article 6.

Guidance and sources for action

1. Technical Guide for the assessment and prevention of risks related to chemical agents present in workplaces — INSST, 2022
2. Chemical risks: information on sensitizers, exposure assessment and control — INSST
3. Guidance on the Application of the CLP Criteria — ECHA
4. Classification and Labelling Inventory — ECHA

Classification

The classification of substances and mixtures as sensitizers is established by Regulation (EC) No 1272/2008 (CLP) on the classification, labelling and packaging of substances and mixtures. The Regulation remains in force and EUR-Lex currently provides its consolidated version as of 1 July 2026.

Regulation (EC) No 1272/2008 (CLP) — current version on EUR-Lex

Skin sensitizers

Substances may be classified as:

1. Category 1, when they meet the criteria for skin sensitization and there are insufficient data for subcategorization.
2. Subcategory 1A, for substances considered strong skin sensitizers.
3. Subcategory 1B, for other skin sensitizers.

Classification is based on an assessment of the available evidence, including human data and, where appropriate, the results of suitable animal studies.

Signal word: Warning

Hazard statement:

H317: May cause an allergic skin reaction.

Pictogram: GHS07 (exclamation mark).

Respiratory sensitizers

Substances may be classified as:

1. Category 1, when they meet the criteria for respiratory sensitization and there are insufficient data for subcategorization.
2. Subcategory 1A, for strong respiratory sensitizers.
3. Subcategory 1B, for other respiratory sensitizers.

Classification is carried out by assessing the available evidence in accordance with the criteria established in the CLP Regulation.

Signal word: Danger

Hazard statement:

H334: May cause allergy or asthma symptoms or breathing difficulties if inhaled.

Pictogram: GHS08 (health hazard).

The hazard statements H317 and H334 remain part of the current CLP system.

Legislation

Law 31/1995 of 8 November on Occupational Risk Prevention — consolidated text of the BOE Law 31/1995 of 8 November on Occupational Risk Prevention — consolidated text of the BOE

Royal Decree 374/2001 of 6 April on the protection of the health and safety of workers against risks related to chemical agents at work — consolidated text of the BOE Royal Decree 374/2001 of 6 April — consolidated text of the BOE

Regulation (EC) No 1272/2008 (CLP) on the classification, labelling and packaging of substances and mixtures — EUR-Lex, current version Regulation (EC) No 1272/2008 (CLP) — EUR-Lex, current version

References

The main official sources used to update this section are:

Last content update: August 2026.