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Description of key information

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (not sensitising)
Additional information:

Sulphur trioxide will react rapidly with atmospheric moisture and moisture in the skin to produce sulphuric acid.

Sulphur trioxide and sulphuric acid have been in industrial use for many decades, and skin burns resulting from accidental occupational dermal contact with concentrated sulphuric acid are well documented.  However, skin sensitisation secondary to skin irritation or burns has never been described, despite the fact that severe chemical irritation and burns are known to create favourable conditions for the induction of contact allergy: this strategy is, in fact, employed in routine skin sensitisation testing protocols such as the Magnusson and Kligman maximisation test.  Repeated contact with more diluted sulphuric acid is known to cause skin desiccation, ulceration and chronic purulent inflammation around the fingernails, however these symptoms are quite different from those seen in acute or chronic allergic dermatitis.  Skin contact with weak solutions of sulphuric acid (~10%) has been quite common in the viscose rayon industry for nearly a century, however sulphuric acid allergy has never been reported.  Sulphate ions are considered to be highly unlikely to cause allergy, since the body contains large amounts of sulphate ions (~0.33 mmol/l in serum and about 50 times higher concentration intracellularly).  Various metal sulphates (e.g. nickel sulphate, cobalt sulphate) are used in routine allergy testing, but positive reactions are related to the metal ion, not to the sulphate, as can be deduced from the definitely non-allergenic zinc sulphate.  Similarly, the hydrogen ion has no potential to cause skin sensitisation, therefore protein binding and hapten formation is considered to be highly unlikely.

Based on the information discussed above, it can be concluded that sulphuric acid has no potential to cause delayed contact hypersensitivity (skin sensitisation in humans) is not an allergen in humans.

Animal testing for sensitisation potential is not scientifically justifiable as it would not provide any information relevant for the human risk assessment and, additionally, testing with a corrosive substance is not required and cannot be justified on animal welfare grounds.


Migrated from Short description of key information:
No animal studies of skin sensitisation are available.

Respiratory sensitisation

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (not sensitising)
Additional information:

Exposure of laboratory animals to sulphuric acid aerosols has been associated with non-specific airway hyper-responsivity, including bronchial constriction. However these effects do not have an immunological mechanism and therefore do not represent respiratory sensitisation.

Similar effects following the inhalation of sulphuric acid aerosols/mists have been seen in exposed humans and asthmatic subjects have proved to be more sensitive than non-asthmatics to effects including bronchoconstriction. It is thought that findings may be due to the lower pH of the respiratory mucus in asthmatics (pH 5.3 -7.6) compared to non-asthmatics (pH 7.4 -8.2). This has the consequence that the the buffering capacity of respiratory mucus is lower and also that the mucus is more viscous, thus reducing the efficacy of mucociliary clearance. Asthmatic subjects (and also non-asthmatics with hyper-responsive airways) are therefore inherently more sensitive to the local effects of sulphuric acid (and other acid) inhalation on the respiratory tract, however the effects do not have an immunological basis and therefore do not represent respiratory sensitisation (occupational asthma).


Migrated from Short description of key information:
No studies are available.

Justification for classification or non-classification

No classification is proposed for skin sensitisation or respiratory sensitisation based on theoretical considerations and in the absence of any findings in exposed humans following occupational use over a long period of time.

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