Localized deficiency of folate and B12 made cells more susceptible to carcinogens present in tobacco smokeSmokers have lower serum B12 levels than non‐smokersB12 levels are lower in squamous cancer cells (3.98 ± 1.3 pg μg‐1 DNA) than in adjacent non‐infected tissue (8.83 ± 1.3 pg μg‐1)Lower DNA methylation in squamous cell cancer cellsDecreased activity of MTHR. The gene discussed is DNAJC10; the disease is squamous cell carcinoma.