Spray used by the police to control violent criminals is more damaging than thought, research shows.
The spray incapacitates aggressors
Streaming eyes, burning sensation, and blurred vision were commonly reported to doctors treating people who had come into contact with the spray.
But blistering, swelling, and skin inflammation also occurred.
The London Medical Toxicology Unit team said, in the Emergency Medical Journal, that the police should consider using weaker formulations.
"Personal incapacitant" spray (PIS) has been used by English and Welsh police forces since 1995 for self defence in situations where "lethal force is inappropriate."
It combines the compounds CS (o-chlorobenzylidine malononitrile) dissolved in the solvent MiBK (methyl iso-butyl ketone).
Its effects are designed to be short-lived, subsiding within 30-60 minutes.
But research by the toxicologists attached to Guy's and St Thomas' Hospital in London suggests symptoms could be longer lasting.
They collected information on 277 cases of PIS trauma submitted from healthcare professionals to the National Poisons Information Service in London for the first nine months of 1998.
Almost two thirds of incidents were the result of an encounter with the police. The remainder had been sprayed by other people.
Most spray was in the eyes or on the face, but in roughly a third of cases, the spray was breathed in.
Streaming eyes, burning sensation, and blurred vision were most often reported.
But blistering, swelling, and skin inflammation also occurred and were significantly more common among people who had been sprayed by the police
More of these patients were referred for further specialist treatment and had waited six or more hours after the incident to seek help.
This suggests that either their symptoms were more severe, or that fear and/or arrests kept them from seeking help, said the researchers.
"CS preparation used by the UK police may cause more adverse effects than other PIS preparations.
"A detailed study is now required into the potential adverse effects of the CS used by police," they said.
They suggested less concentrated or differently formulated CS gas should be considered.
A Home Office spokesman said the work had been reviewed by the Department of Health Committees on Toxicity, Mutagenicity and Carcinogenicity in September 1999.
"The cases referred to in this report must be taken in context with the number of times CS was actually used.
"It estimated that the total number of complaints was in the region of 5% of the number of times the spray was used."
He said those presenting themselves for medical attention were likely to be a very small percentage of those sprayed during the period of the study.
But he added: "Work is continuing to identify suitable alternative solvents but this is a necessarily slow process. It is important to ensure that any new solvent would not present additional risks to the user or the public.
"There is also an active programme to identify and evaluate other less lethal technologies to provide officers with a range of alternatives to suit the operational situation," he said.