The Court has decided that symptomless sensitisation is an injury. But there may have been some error.
IgE sensitisation to platinum salts was detected by a routine skin prick test in five employees. Occupational exposure was the probable cause. The employer admitted breach of statutory H&S duty.
Sensitisation is a necessary precursor to allergic reaction, but a person may remain free of symptoms for years and may never have an allergic reaction. What the Court seems not to have been advised though is that in a high proportion, sensitisation becomes undetectable if further contact with the allergen is avoided or remains below a certain level.
There were no symptoms despite working in the same environment which had caused this biological change. It is implausible that all five became sensitised only moments before the test. More likley they were sensitised at some point between tests and had continued to be exposed to platinum salts until the test. This should have alerted the Court to the possibility that sensitisation is reversible and to ask why the expert testimony had not said so.
The employer had a union-negotiated policy of transferring sensitised employees away from further exposure to platinum salts. Compensation for loss of income could be applied for. In other workplaces with other employers, sensitised people choose to continue as normal and if they become allergic they then decide if the allergy can be coped with. If not coped with, they are redeployed.
The claimants sought to show that sensitisation was an injury for the purposes of a claim in tort.
The judgment focuses on two precedents where physical/biological changes had occurred but with no symptoms. These are Cartledge (symptomless pneumoconiosis) and Rothwell (symptomless pleural plaques). Much effort was expended on deciding that Rothwell did not apply.
In Cartledge v E Jopling & Sons Ltd  AC 758 it was decided that an injury (symptomless pneumoconiosis) which the plaintiff had no present knowledge of or reason to note was an injury for the purposes of the Limitation Act (1939). If looked for, physical changes would have been discovered. Under aerobic activity extremes, limitations of fitness would have been noted, risk of TB would have been higher. At some point, the pneumoconiosis could have become symptomatic.
Cartledge relates to irreversible (possibly progressive) injury (pneumoconiosis) which would inevitably, by the nature of its present physical form, be discovered by extreme exercise, and not in the short-term by working in a dusty workplace. The pathology physically prevents the full capacity of the lung to be applied and always would do so if the pathology was more than de minimis.
The Court sought to apply this precedent and in doing so made the following incorrect statements (my emphasis added):
A person who has been sensitised but has not yet developed symptoms is not limited in any way in their life, except that they must avoid circumstances in which they are exposed to platinum salts. Platinum salts are not encountered in everyday life, only in certain specialised workplaces. Sensitised people cannot work in jobs which involve the potential for further exposure.
Expert evidence would have advised that must and cannot do not apply. Actions are optional.
The parallels with Cartledge fall away: Sensitisation without allergy is undetectable unless looked for (pneumoconiosis can always be discovered). Sensitisation is reversible (pneumoconiosis is not). Sensitisation can progress to a higher state without becoming allergy and then once more become undetectable (pneumoconiosis goes in one direction only). Sensitisation remains symptomless sensitisation, but may be transformed into allergy (i.e a different state) (pneumoconiosis remains pneumoconiosis). Had the Court been aware, they may have decided to do without the support of Cartledge.
Without some distortion of Cartledge, sensitisation is just a marker of increased vulnerability. It indicates increased risk of injury. Risk of injury is not injury.
In practice, insurers usually paid sensitisation claims anyway. But they didn’t have to. The Supreme Court may have felt that their decision merely formalised what was once optional but routine insurance industry practice.
Without Cartledge, if on closer examination it is found not to apply, the Court has effectively decided that combining risk of injury (in this case manifest as a biological response) with policy responses is now an injury. Risk of injury and operative policy = injury. Where and is a logic operator.
If so, employers will need to re-evaluate the purpose of routine audiometry, tests of vulnerability to PTSD, the use of skin prick tests, the use of genetic and epigenetic markers for injury vulnerability, and so on. They will also need to evaluate the implications for disability discrimination if vulnerability to impairment is to be regarded as actually having the impairment.