There has long been a saying that eating soy sauce can darken the skin, and some people believe that consuming it when you have a wound can cause the scar to become darker. Experts in nutrition and dermatology both state that the components in soy sauce have no relationship with melanin, the pigment that darkens the skin, and eating soy sauce does not cause the skin to darken.
Gao Jian, Director of the Department of Nutrition at Zhongshan Hospital Affiliated with Fudan University, pointed out that soy sauce is mainly made from soybeans, starch, and wheat flour through fermentation. After being consumed, these components become colorless mixtures of amino acids and peptides. The reason for this saying might be the association with the color of soy sauce. In fact, the black color of soy sauce comes from the caramel color it contains and does not promote melanin formation.
Shu Chang, a dermatologist at Peking Union Medical College Hospital, stated that the main factors affecting skin color are genetics, ultraviolet (UV) rays, and medication. Among these, 60% to 70% is genetic. Among后天 (postnatal) factors, sun exposure has the greatest impact on skin color. UV radiation promotes a chemical reaction in melanocytes, leading to an increase in melanin in the skin. Furthermore, some diseases and medications can also cause the skin to darken. For instance, tetracycline and anti-rheumatic drugs can affect the activity of tyrosinase in the blood, leading to abnormal metabolism in melanocytes. Other drugs, such as the antiarrhythmic amiodarone, can bind with amino acids and proteins in the body to produce colored substances that affect skin color.
Many people have the experience that after a wound heals, the scar is darker. Is it then inadvisable to eat dark-colored foods like soy sauce? Shu Chang clarified that when the skin is injured, melanin can transfer from epidermal cells to dermal cells. The metabolic rate of dermal cells is slower than that of epidermal cells, so the color remains. This has nothing to do with foods like soy sauce.
However, some photosensitive foods can indeed have an effect on the skin, such as celery, figs, and cilantro. It is recommended to avoid prolonged sun exposure after consuming them to prevent phototoxic reactions, which can lead to post-inflammatory hyperpigmentation. Additionally, if you have a wound, you should avoid prolonged sun exposure, as UV rays can easily activate melanocytes, making the skin more prone to darkening.