vitamin B12 may boost acne by disrupting a type of skin bacteria known as Propionibacterium acnes that's related to acne
One lesser-known sign of B12 deficiency is dark knuckles. According to a study published in the Indian Journal of Hematology and Blood Transfusion, dark knuckles can be an important marker for vitamin B-12 deficiency. According to the research, sometimes it may be the only marker for B12 deficiency.
The hyperpigmentation related to vitamin B12 deficiency is more common in darker-skinned patients. Few other cases of skin hyperpigmentation due to vitamin B12 deficiency have been reported in the literature. The mechanism of hyperpigmentation is due to increased melanin synthesis rather than a defect in melanin.