The first place tobacco often shows its damage is not the lungs. It is the mouth. If you smoke, your gums face a daily chemical assault. Over time, that can turn mild irritation into a chronic disease that loosens teeth and eats away at bone. Scientists have long known smoking makes periodontitis worse. The condition is a severe, ongoing inflammation of gum tissue. It starts when microbes slip into the gums and the immune system reacts in an unhealthy way. As the reaction continues, gums pull back. The bone that anchors teeth weakens. Teeth can loosen and fall out. Now, researchers say they have pinned down key cellular changes that help explain why smokers often develop faster, more severe disease. A team from Sun Yat-sen University in China used a high-resolution method to map gene activity in gum tissue. Construction of a single-cell resolution spatial transcriptomic atlas of human gingivae. (CREDIT: International Journal of Oral Science) The study points to a chain reaction that begins at the gum surface, spreads through support cells, then escalates …