Some people have proposed using that hotter than hot capsaicin extract for use against sharks. The idea behind one Capsicum shark repellent patent is essentially a pepper spray for sharks. Delivering a shot of Capsicum juice at a shark would irritate the fish's gill membranes and nerves across its entire body [source: Matos and Romero]. Similar types of repellents have worked with terrestrial pests, such as deer and even bears. However, the patent application has yet to be approved, calling the invention into question.
Because of the sharks' sensory organs and the dilution of capsaicin in the water, it doesn't seem likely that the pepper spray would deter the fish. Their noses don't open into their respiratory systems like humans, meaning any spicy water would not enter through the nostrils [source: Parker]. They also wouldn't ingest the water because they extract oxygen from it then release it through their gills [source: Parker]. Finally, their eyes have dual eyelids and a protective membrane to keep their peepers safe.
The Discovery Channel's dynamic duo of science, Jamie and Adam of MythBusters, closed the book on this question when they tested this theory with capsaicin extracted from the fiery habanero pepper inside of a bio-degradable balloon. Even though the peppers pack a powerful punch, it wasn't enough to scare away any sharks.
But these results aren't that surprising considering the amount of noxious chemicals sharks can withstand. For example, one experiment to find a poison capable of killing a shark ended in 29 misses [source: Parker]. Strychnine was the only thing that did the job, and even that took eight minutes to work [source: Parker].
Fortunately, shark attacks are a statistically rare occurrence, and there are many things you can do to help avoid encounters and to fend them off when you come face to face.
For more information about shark defense and other shark-related topics, dive into the links on the next page.