Rumor: Will eating soy sauce blacken skin wounds?
Truth: This statement makes no sense.
The color of skin is determined by a substance called melanin in the body. Melanin is mainly produced by a series of complicated reactions of the amino acid tyrosine.
Soy sauce does contain [tyrosine]. But the content is very small. In fact, its content is not even comparable to milk, soybean milk, Job’s tears, etc.
Moreover, soy sauce is neither particularly rich in melanin raw materials, nor can it promote melanin synthesis. Naturally, it will not blacken skin or wounds.