Musth (in bulls) and estrus (in cows), are natural phenomena caused by a surge in reproductive hormones. Although musth lasts for months in some males, the female is fertile for no more than a few days each year. Males will have a much more violent condition, often in the cold season between December and February. Musth occurs in healthy elephants 20 years and up, throughout their reproductive life.

When a bull elephant comes into musth, a change occurs in the small glands on both temples between its ears and eyes. The glands will be swollen as big as eggs for many days. Lily fluid will start to flow from the glands (which normally cannot be seen at all), and then a sticky fluid with a very strong smell is secreted. During the musth period, the bull will be aggressive, difficult to manage and dangerous, even to their mahout. When charging, the elephant will curl up its trunk and stab with its tusks. When attacking, it will grab with its trunk and stamp or kick with its feet, or attempt to roll the victim back and forth on the ground.

The causes of musth have not been clearly established. It is generally understood that elephants need to mate and to claim their won territory, and musth may be a natural mechanism for selective breeding. To safely deal with musth, mahouts tether the elephant in an isolated place with sufficient food and water, and avoid making it work hard.