With the increased use of pepper spray to subdue protestors from coast to coast, the nonlethal weapon is receiving extensive media attention from pundits, and it is worthwhile to take some time to analyze the health effects of pepper spray. Elsewhere people may consider the impact of the spray on respiratory health, permanent alteration of pain response, and possible death. Here we will consider what we know about the impact of pepper spray on the human cornea as well as the conjunctiva.
What we know about possible eye injury from pepper spray seems to be surprisingly limited. The product has never been evaluated by a regulatory body for human health and safety, so accounts of its eye safety remain largely anecdotal, based on very few limited studies on humans and animals. How few studies? Probably less than a dozen looking at eye safety. How limited? The total number of human subjects is probably less than 100, not enough for a single decent study, let alone the basis for declaring any substance “safe.” I say “probably” because I am allowing that my limited research on the NCBI database may have missed some studies, but I only found four studies looking at human corneal exposure, with a total of 62 subjects.
Two studies report the impact of pepper spray on 57 volunteers. According to one study, which used pre- and post-exposure visual exams at 10 minutes, 1 hour, and 1 week. This study found that among its 47 subjects visual acuity was unaffected by pepper spray exposure. Although corneal sensitivity was reduced at 10 minutes and 1 hour, it had returned to baseline by 1 week after exposure.
A second study looked at the impact of pepper spray on 10 volunteers. It also reported that the corneal response to a first exposure to pepper spray is primarily temporary swelling of the cornea’s outer layer, with no impact on the cornea or its nerves, though tear fluid showed increased levels of nerve growth factor, showing that nerves were responding to the stress, though sprouting of nerves was not observed. However, one volunteer did lose one line of best corrected visual acuity. This study concluded, however, that a volunteer who had been exposed to pepper spray before showed an unusual arrangement of nerve fibers.
In both of these studies, one week follow-up time is too short to evaluate the impact of pepper spray on the cornea. In many circumstances, such as coronary nerve recovery following myocardial infarction, nerve recovery may begin almost immediately, but studies of corneal healing after LASIK indicate that corneal nerves may not begin to recover until six months after injury.
The other two studies looking at the corneal impacts of pepper spray are evaluations of exposure victims who suffered serious adverse consequences of exposure. One study evaluated four individuals who suffered corneal erosion due to pepper spray exposure. The primary culprit in all four cases was not the oleoresin capsicum, the so-called “pepper,” but the carrier agents. In fact, one victim was exposed to a mock pepper spray with only carrier and no actual oleoresin capsicum. In this study, all four patients showed “a long-lasting, deep corneal and conjunctival erosion,” which resolved partially, but full healing of the cornea’s deeper layers does not generally restore the cornea to its original form (which is what makes LASIK treatment generally permanent). In this study, researchers also used pepper spray on a soft contact lens and plastic cup to demonstrate the erosive effects of the carrier.
The fourth study looked at a 2.5 year old boy who suffered conjunctival proliferation after accidental exposure to pepper spray. Conjunctival proliferation is when the outer layer of the eye sprouts additional growth, such as a pterygium. This growth began three weeks after exposure, and had to be surgically removed. Once removed, the growth did not recur during three months of follow-up.
Although conventional wisdom suggests that pepper spray is largely safe for use in subduing arrest subjects, there is actually little evidence to support this supposition, and certainly enough evidence to suggest that it should be evaluated clinically in larger populations with longer follow-ups to ensure it is actually reasonably safe.
In the meantime, if you have suffered pepper spray in the eyes, you should be evaluated by your eye doctor, even if you do not believe you have suffered any lasting effects.