Some of the noncancerous causes of lumps in the mouth include warts, oral thrush, a torus and salivary gland tumors, notes Merck Manuals. Some precancerous causes of lumps in the mouth include leukoplakia and erythroplakia. These are often flat white or red spots that lead to oral cancer.
Warts can appear in the mouth if a person sucks or chews one on his fingers, and they can also occur as a sexually transmitted disease after oral sex, states Merck Manuals. Thrush is a common yeast infection in people with diabetes, weak immune systems and people who take antibiotics. A torus is a harmless projection of bone that grows slowly in the mouth.
Salivary gland tumors are often benign and painless growths that usually sprout on the inside of the cheek, states Merck Manuals. They most often occur in women over the age of 40.