The Ninja Were Aromatherapists
You now know that the ninja possessed advanced pharmacological knowledge. Fundamental to this knowledge was a keen sense of smell which allowed the ninja to distinguish between different herbs. That is why the ninja were also highly sensitive to the smells of incense. The ninja used the aromas of sandalwood, agallochum, cedar wood and other incense in order to improve mental control.
The effects were real, and the ninja practiced what would nowadays be called aromatherapy.
Ko no Juttoku (The Ten Virtues of Incense)
To a greater or lesser extent, incense influences spirits, cleanses the mind and body, removes poison, relieves drowsiness, is a friend when one is alone, and provides rest when one is busy. It can also be kept for long periods without rotting and may be used on a regular basis.