Porcupines typically regrow quills to replace the ones they have lost. The new quills generally start to grow back within days after they fall off.
Porcupine quills are similar to human hair in several ways, including the fact that they often shed. However, the animal may also lose the quills in an attack. A porcupine's quills typically sit flat until the animal is threatened. Although the porcupine cannot shoot its quills, the quills come unattached quite easily when they are touched. Whether the animal sheds its quills or loses them in an effort to ward off predators, new successor quills begin to regrow within a few days. These quills grow quite quickly, usually one millimeter per every few days until they reach their full length.