This phase I trial studies the side effects and best dose of photodynamic therapy using aminolevulinic acid in treating patients with oral leukoplakia. Photodynamic therapy uses a drug, such as aminolevulinic acid, that becomes active when it is exposed to a certain kind of light. When the drug is active, abnormal cells are killed. Photodynamic therapy using aminolevulinic acid may be effective against oral leukoplakia.