What happened to the yellow beard?

Beard is a male characteristic after men enter puberty. Beard is originally black, but some people find that it slowly turns yellow. There are generally several cases: 1, congenital genetic reasons. 2, malnutrition, mainly caused by high malnutrition. 3, lack of trace elements, such as copper deficiency, can cause beard yellow. 4, disease factors, such as suffering from certain diseases, iron deficiency anemia and hypothyroidism, or some major disease recovery stage, these can show that the beard slowly turns yellow. The above health science knowledge is for reference only, the specific situation needs to be checked in a regular hospital, and judged by a professional doctor.