Antlers are found on the heads of male members of the deer family (with the exception of the reindeer, where the females also sport the pointy headgear). They're made of bone and sprout from the pedicle, a bony platform-type of growth located just above the animal’s skull.
Antlers begin growing in late April, and usually reach full size by August. While they’re growing, the antlers are covered with “velvet,” a fuzzy layer of flesh that supplies blood to the bony growths. Once the antlers are fully grown, the velvet dries up, and the deer strips it off by rubbing against a tree.
During mating season, males use their racks to fight other males; the bigger a male's antlers, the more likely he is to find a mate. When the season ends, usually in late December, the entire pedicle breaks loose from the deer’s head and his antlers are shed as a complete set. And while shed antlers make trendy coat hooks, you’re upsetting the balance of nature if you bring them home: Mice, squirrels, porcupines and other small animals all eat the discarded antlers in order to get much-needed calcium.
Horns, on the other hand, grow constantly throughout the life of the animal (goats, sheep, oxen, and bison) and are never shed. Horns consist of tubular filaments of keratin, the same substance found in human hair and nails. Unlike antlers, horns only have one point (save for the pronghorn sheep), and if a point tip is broken off, it never reforms and remains blunted.