Some caterpillars have specialized urticating, or stinging spines that connect to poison glands containing toxins. They use these spines in defense against predators. Most occurrences of human contact with the spines are accidental. Upon touching the spines, they break and either penetrate the skin allowing the toxins to flow or they spread the toxins on the surface. The poison can cause reactions such as a stinging sensation, itching, burning, and even intense pain. Reactions depend on the species and thier toxin, type of contact and any allergies that a person may have.