Studies have found that long-term exposure to aromatic chemicals, such as dyes, leather, rubber, and paint, may increase the incidence of bladder cancer. Smoking is also an important cause of bladder tumors. Smoking can cause abnormal tryptophan metabolism in the body, and the abnormal metabolism of tryptophan can produce metabolites such as 3-hydroxy-2-aminoacetophenone, which are excreted by the bladder and can promote bladder cancer. In addition, long-term local stimulation of bladder mucosa may also induce cancer. Long-term chronic local irritation of bladder wall, such as long-term chronic infection, bladder stones, long-term stimulation of parasitic diseases and urinary tract obstruction, may be factors that induce cancer. In contrast, adenoidal cystitis and mucosal leukoplakia are precancerous lesions of bladder cancer.