Three different studies report that fermented soy milk inhibits melanin production—the pigment responsible for dark spots. This was discovered when researchers tried to find a solution for the unesthetic browning in mushrooms. 

Like in humans, the browning is caused (to a part) by the enzyme tyrosinase. For that reason, most brightening cosmetics are trying to suppress tyrosinase activity in skin pigmentation disorders like melasma.

Especially soy milk fermented with the probiotic strain Lactobacillus plantarum controlled melanin production and tyrosinase activity effectively [1].

Soy contains a powerful skin brightener called daidzein—an isoflavone found in legumes. Daidzein and its metabolite equol exert their lightening effect by blocking overactive tyrosinase and melanin production. A study found that the fermentation of soy increases the potency of these two components up to 9 fold and makes them more bioavailable, therefore very effective in skin brightening [1][2].

Another skin brightener and tyrosinase inhibitor in fermented soy milk (with L. plantarum) is uracil—famously known as a part of RNA [3].

I found a website with instructions how to make fermented soy milk.

https://lightorangebean.com/how-to-make-soy-milk-kefir/

Instructions

I would drink a small glass daily on an empty stomach in the morning and apply some on the skin before bedtime.

In the light of critics on soy due its estrogenic effects with concerns to cancer, I wanted to share something interesting. I remember a gynaecologist explaining that the estrogen in soy is not causing an increase in the type of estrogen responsible for cancer. I do not remember the source but I found a map that shows the demographics of breast cancer worldwide. If you look at China and Japan where people eat tofu (cheese from soy) daily, you see that the breast cancer rates are very low (see 2nd image https://www.researchgate.net/publication/349217393_Global_incidence_and_mortality_of_breast_cancer_a_trend_analysis).

Please buy non-GMO, organic soy milk without additives and consume it fermented as described in the link above.

I hope this helps. Please share your results if you are trying it.

1. Chen Y-M, Shih T-W, Chiu CP, Pan T-M, Tsai T-Y. Effects of lactic acid bacteria-fermented soy milk on melanogenesis in B16F0 melanocytes. Journal of Functional Foods. 2013;5:395–405.

2. Chang C-J, Tsai T-Y. Antimelanogenic effects of the novel melanogenic inhibitors daidzein and equol, derived from soymilk fermented with Lactobacillus plantarum strain TWK10, in B16F0 mouse melanoma cells. Journal of Functional Foods. 2016;22:211–23.

3. Chang C-J, Dai R-Y, Leu Y-L, Tsai T-Y. Effects of the melanogenic inhibitor, uracil, derived from Lactobacillus plantarum TWK10-fermented soy milk on anti-melanogenesis in B16F0 mouse melanoma cells. Journal of Functional Foods. 2015;17:314–27.