Evidence check: B12 in the context of Haut

The evidence for vitamin B12 in the context of skin health is limited and largely mechanistic. Severe B12 deficiency can cause dermatological signs such as hyperpigmentation, vitiligo, or angular stomatitis, but these are rare in well-nourished populations. In individuals without deficiency, B12 supplementation has not been shown to improve skin appearance or conditions. Some consumer DNA tests claim links between B12-related genetic variants (e.g., MTHFR, FUT2) and skin issues, but the effect sizes are small and the evidence is inconsistent. Therefore, the evidence level is 'mechanistic': plausible biological pathways exist, but robust clinical trials are lacking. Before supplementing, a blood test (holotranscobalamin or MMA) is recommended, as high-dose B12 may be unnecessary or even harmful in certain conditions (e.g., kidney disease). Consumer genetic tests can provide hints but not definitive answers.