If gray hair becomes black due to deficiency of kidney essence, you can take Huang Jing; if gray hair becomes black due to other reasons, taking Huang Jing is not very effective. However, there is no authoritative information to record the time to eat yellow essence to make gray hair black. Huangjing is the dried rhizome of Dian huangjing, Huangjing or multiflora huangjing of the lily family, sweet in flavor, flat in nature, belonging to the spleen, lung and kidney meridians. It has the effects of benefiting qi and nourishing yin (tonifying qi and nourishing yin fluid), strengthening the spleen and moistening the lungs, and tonifying the kidneys and benefiting the essence (replenishing kidney essence in the body). Huang Jing can be used to treat spleen and stomach qi deficiency, laziness and weakness, stomach yin deficiency (insufficient yin fluid in the stomach), dry mouth with little food, lung deficiency with cough, coughing up blood and hemoptysis, deficiency of essence and blood, lumbar and knee soreness and tenderness (a feeling of soreness and weakness in the lumbar and knee areas), premature graying of black hair, internal heat and thirst (heat in the body accompanied by symptoms of overeating and excessive urination), and other symptoms. It should be noted that it is not suitable for those with spleen deficiency and dampness, phlegm-dampness congestion, or Qi stagnation and abdominal fullness, and adverse reactions are not known. If you need to take Huang Jing, it is recommended to consult a healthcare professional.