Once, a friend was doing an essential-oil back massage, and a 30-year-old female therapist told me: “I think you’re a little lacking in kidney qi. The kidney-deficiency marks on your back are very obvious. I’ll use an essential oil that warms the kidneys for you and give you a good massage.” At that time, the friend was only 20 years old. That was the first time the friend knew that he was lacking in kidney qi.