White sponge nevus

White sponge nevus is a rare, benign inherited condition in which thickened, velvety, sponge-like white patches form on the moist lining of the body, most often on the inside of the cheeks. Several patches usually appear, and they can also occur, rarely, in the nose, esophagus, genitals or anus. The patches are caused by a noncancerous overgrowth of epithelial cells and may be present from birth, though they usually first appear in early childhood and can change in size and place over time. They are generally painless, but folds of extra tissue can encourage bacterial growth and infection, and the altered look and texture bothers some people. Variants in the KRT4 or KRT13 gene make keratin proteins that fit together poorly, so the mucosal filaments are easily damaged. The condition is inherited in an autosomal dominant pattern with reduced penetrance and is estimated to affect fewer than 1 in 200,000 people worldwide.